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Having recently seen a Martello tower on the East coast of England, I tried to find-out what the defensive strategy was supposed to be - but the internet seems very short on information.

The South-East coast of England had 103 of the towers covering a coastline of, maybe 500 miles..? This would put them an average of 5 miles apart. I'm assuming that the artillery of the time would not be able to fire a distance of 2.5 miles - and if they could, it would be extremely inaccurate.

If I were an invading Navy, I would give the towers a wide berth, then I would land my ships at a point equidistant from 2 towers where they would not be able to reach with their cannon, then move inland within this narrow corridor, leaving the towers until they surrendered or starved.

I assume I'm NOT the greatest military mind in history, so, what am I missing?

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    England is not the only place where Martello towers were constructed. Four Martello Towers were also constructed around Kingston, Ontario, as part of the Old Fort Henry and Fort Frederick defenses of Kingston Harbour - at least one of which is open in summer as a museum on the lake shore near Queen's University. – Pieter Geerkens Jul 9 at 18:50
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    Indeed. The Wikipedia page says the British basically stole the idea after having had a hard time defeating a tower in Corsica in 1794. – Lefty Jul 10 at 9:49
  • A possible explanation os such construction is that protection is generally focussed only on strategic locations (ports, villages). So if you imagine this as every single village gets a fortress it immediatly sounds like a very generous defense. – Greg Jul 11 at 6:59
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That was the whole idea behind it. Not every bit of coastline is liable to invasion. Only on certain beaches troops could be landed. Steep cliffs and dangerous shallows didn't need protection. Place a very strong defense tower with a gun crew, and that single gun crew could keep a possible invasion force at bay. Don't forget that coastal defense has the advantage of stability - the earth (hopefully) doesn't move as much as the waves do. They had a much better chance of hitting their target than any naval vessel. Not to mention they had all the time in the world to pre-plan possible targets.

One Martello tower with a crew of, say, 20 could (at least in theory) keep several heavily armed warships with many hundreds of crew away.

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    Great answer, thank you. I never considered the possibility of natural hazards within the sea making certain areas much more difficult to land troops. The tower that I saw was the one in Aldeburgh, Suffolk. To the untrained eye, the coastline looks like all the rest for miles in either direction - this is what raised the question in my mind. – Lefty Jul 9 at 9:38
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    Even if you can't build a Martello to cover every possible invasion site, if you build them to cover the best ones then you are forcing the invaders to use worse places (probably very much worse) and making them vulnerable to attacks from your mobile troops. Plus landing on beaches is hard, and virtually all invasions try to capture a port early on in order to speed up landing troops and supplies. If a tower can prevent that it's helped a lot. – DJClayworth Jul 9 at 15:55
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    Good answer, and just to point out, OP said "...then I would land my ships at a point equidistant from 2 towers where they would not be able to reach with their cannon, then move inland within this narrow corridor..." - That's part of the point. Now the invading army is going through a "bottleneck'ed" area, which the defending army can prepare defenses for inland. – BruceWayne Jul 9 at 17:33
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    To quote Nelson - who knew a thing or two about naval warfare: "A ship's a fool to fight a fort." Remember that while 3rd rates and up would carry 32 lbers the same as a fort - a ship has great difficulty aiming those guns at a fort that might be 50 or more feet higher in elevation. That height advantage also gives the fort's guns significantly greater range. – Pieter Geerkens Jul 9 at 18:37
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    @Lefty Bear in mind that the modern coastline around Aldeburgh is not the same as the historical one. Historical maps show the river estuary has moved about 1 mile per 100 years. In some parts of the east coast of England, even with modern erosion control methods the coastline is eroding more than one meter per year. – alephzero Jul 9 at 22:09
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I think that the towers have to be considered in context. They were just part of the defenses, which included gunboats and inland fortifications, that were intended to repel a French invasion during the Napoleonic Wars. While modern historians can look back with hindsight and declare that the risk of a French invasion evaporated after Trafalgar, people on both sides of the Channel continued to take the threat of an invasion seriously almost to the end of the Wars.

The French plans involved moving an army of fifty to a hundred thousand men (along with artillery, horses and supplies) across the channel to invade. To bring these ashore to form an effective offensive force, the landings needed to be comparatively concentrated, which limited the potential landing sites. These had to avoid hazards both at sea and on the beaches, that might cause losses of vessels and their cargo or bottlenecks in getting the men and materiel off the boats.

The invasion vessels wouldn't have the advantage of motor power so they would have to be sailed and/or rowed up to the beaches. The majority of the vessels built for the invasion were, therefore, relatively small and of shallow draught. While that enabled them to come right up onto the beaches, it also meant that they weren't very seaworthy.

The British Royal Navy was larger than the French Navy and was viewed by the British as the first line of defense. The purpose of the Trafalgar campaign in Napoleon's planning was to bring a large part of the French fleet together in order to have a local advantage in numbers over the British. The hope was that they could hold off the British warships long enough to get the invasion vessels across.

As a consequence, a long sea crossing wasn't very desirable. The longer the vessels were in transit, the larger the chance that either the Royal Navy or mother nature would send the craft to the bottom. This further limited the potential landing sites and this was understood by planners on both sides. Therefore the towers were (comparatively) concentrated at these locations.

In the end only 73 towers were built in the Southern District - 27 in Kent and 46 in Sussex; but this was enough to defend the threatened beaches with chains of towers spaced at intervals of 500-600 yards. That distance left no point which could not be swept with grape- and case-shot from 24-pounder guns, supplemented by some 5½-inch howitzers.

Britain at Bay, pg. 118

The main purpose of the towers wasn't to stop the invasion at the beach but to slow things down to allow the British army and militia to concentrate their forces inland to defeat the invaders. While the single cannons mounted on the towers weren't all that much of a threat to the warships of the French Navy, a direct hit by solid shot was more than capable of sinking the smaller boats that would bring the men and supplies to the shore. The sustained rate of fire of these weapons wouldn't have been particularly great, but the potential for chaos caused by sinking a few vessels and the evasive actions of other boats (many of which would have inexperienced crews), would have slowed and disrupted a landing, causing large numbers of casualties in the process.

…case-shot came in two forms, 'heavy' and 'light'; and it appears that one 24-pounder round of 'heavy case' would contain 84 balls, each weighing six ounces, on 24-pounder of 'light case' contained 232 balls of two ounces' weight and one round of 5½-inch howitzer contained 100 two-ounce balls. This means that a single round of 'heavy' 24-pounder case-shot had nearly the same killing power as a volley of musketry from a company of 100 infantrymen; a single round of 'light' 24 pounder case had more than double the killing power of a volley of 100 infantrymen. Further since, as we have seen, well-served guns could, over short periods, be fired ten or twelve times in a minute, one Martello tower mounting a 24-pounder gun and a 5½-inch howitzer should be able to spray the area of beach it covered with up to 3,300 lethal projectiles per minute. Take these facts together and it seems fair to say that to attempt an assault landing in the face of England's new towers would be courting disaster.

Britain at Bay, pg. 118-119

While I suspect that Professor Glover might have been somewhat over optimistic about the rate of fire from these towers (as I doubt that the garrisons would be drilled that rigorously), it does give an indication of what the towers were theoretically capable of doing.

Further reading:
Britain at Bay: Defence Against Bonaparte, 1803-14, Richard Glover (1973)

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    I question "well-served guns could, over short periods, be fired ten or twelve times in a minute". I have attended competition at Old Fort Henry in Kingston, and the fastest interval time between shots is in the range of 15-20 seconds - making 3 or 4 shots per minute the limit. Considering the necessity to clear the barrel; load and ram powder; load and ram shot / cartridge; then stand clear and fire, I find the notion simply absurd that a rate 4 times what I have witnessed is achievable. – Pieter Geerkens Jul 9 at 18:44
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    @PieterGeerkens Is it surprising that people whose professions it was to operate the weapons would be faster than amateurs with little training and less practice? – Dent7777 Jul 9 at 20:46
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    @Dent7777 A rate of 10 to 12 rounds a minute would require the gun drill to be executed every 5-6 seconds. Given the complexity of this process, I'm doubtful about anyone being able to achieve that rate, let alone be able to sustain that rate over a full minute. The very best ship's gun crews (who were handling similar sized cannon) were quoted at 3-4 rounds a minute, while the average was probably nearer 1-2. – Steve Bird Jul 9 at 20:54
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    @Dent7777: The crews I saw were not amateur, and were well practiced. – Pieter Geerkens Jul 9 at 21:35
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    @PieterGeerkens Do they have day jobs? Is it their profession, operation of period cannon as a unit? I would argue that it is simply not possible to match the level of practice or readiness of active duty, experienced gun crew operators. I concede, ten or twelve times a minute seems unlikely. – Dent7777 Jul 10 at 12:38
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From BBC History site:

Martello Towers were the idea of Captain William Ford of the Royal Engineers and they were sited roughly 600 yards apart and each mounted a long-range 24 pounder cannon. The aim was to cover the most likely landing beaches and to confuse any French landing while British reserves and Royal Navy ships were rushed to the area.

These towers were never tested which is a great tribute. The best defence is that which deters attack and certainly the French regarded these little 'bulldogs' as a formidable barrier. With hindsight it appears that all these defences were, essentially, pointless since Nelson's victory at Trafalgar in October 1805 - at the very moment the construction of the Martello Tower system was getting under way - made a French invasion of Britain a virtual impossibility.

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    I find it difficult to believe they were actually 600 yards apart along the whole of the South-East coast of England - but I can see that at a "likely landing beach", siting them at 600-yard intervals would make an excellent defensive line. – Lefty Jul 9 at 11:41
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    @Lefty: Cliffs are defended by walls of flesh - not walls of masonry. Only the beaches where shallow draft boats could disembark troops needed tower defenses. – Pieter Geerkens Jul 9 at 18:47
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Below is the network of defenses built to protect Kingston Harbour in the 1830's (Old Fort Henry) and 1840's (four larger Martello Towers and Market Battery).

enter image description here

enter image description here

Original 1829 plan for the defenses

Legend:

Large Martello towers:

A. Murney Tower
B. Shoal Tower
C. Fort Frederick
D. Cathcart Tower

Old Fort Henry Complex:

E. West (mini-Martello) Tower
F. East (mini-Martello) Tower
G. Main fort

City Defenses:

H. Market Battery

Note the overlapping fields of fire and the close proximity of the towers. No gap is more than about 600 metres, putting every approach to the harbour or possible disembarking location within about 300 metres of a tower gun.

All of these defenses except the Market Battery (now Battery Park) remain standing, with two (Murney Tower and Fort Frederick on the RMC grounds) open in Summer as museums.

Here is an aerial view (courtesy of Google Earth) looking south-west from Fort Henry in the foreground towards Fort Frederick across Navy Bay, showing the dry moats of the fort and both mini-Martello towers associated with the fort. Note the size difference between the two mini-Martello towers associated with Old Fort Henry (one gun each) and the Fort Frederick and Shoal Towers (three guns each if I recall, plus a larger garrison).

enter image description here

Here is a second view from Fort Frederick in the foreground looking across the harbour to Shoal Tower (right side, half-way up), Market Battery, and Murney Tower (top centre, hard to make out).

enter image description here

As shown here, these towers would be clustered near strategic points - harbours and beaches - so as to provide both overlapping fields of cannister fire against infantry and mutually-supporting round shot against any ships supporting an assault. Placement of the towers on heights (Cathcart Tower and Fort Henry are about 20 metres above lake level, the others lower) extends the range of the guns as well as providing improved sight lines.

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    On initial load & view, I see nothing you refer to. If you can, please increase usability by making that clearer (I can, I think, follow, if I open another view & zoom…) – LangLangC Jul 9 at 19:59
  • @LangLangC: How's this now? – Pieter Geerkens Jul 9 at 20:27
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    Not better for "initial load", but after zooming in on each image it seems to work for me as "just look". (Perhaps compensate for deuteranopic/protanopic people? – The scribble/doodle is hard to match to A with angles and numbers) – LangLangC Jul 9 at 20:32
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    Related? – LangLangC Jul 10 at 8:34
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    This is much more understandable to me. You need to defend a specific area, so you build defenses that can do that. If the towers were built every 600 yards around the South-East of England, the strategy would be obvious - in fact, I would be able to infer that the guns of the day could shoot half that distance. But in this instance, I could just see 20 miles of identical beach disappearing off into the distance - and it suddenly made this tower look quite pointlessly defending this one small section of beach. – Lefty Jul 10 at 9:43
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One factor strangely absent from the other answers is contained in the Wikipedi article: in 1794 the Royal Navy attacked a Martello tower during the siege of San Fiorenzo in Corsica, and found it was unexpectedly hard to knock out. So they copied it. According to the Wikipedia Martello Tower article,

...the British were impressed by the effectiveness of the tower when properly supplied and defended, and copied the design. But, they got the name wrong, misspelling "Mortella" as "Martello" (which means "hammer" in Italian). When the British withdrew from Corsica in 1803, with great difficulty they blew up the tower, leaving it in an unusable state.

The original question asked what the contemplated defensive strategy in England was. One answer could be the towers were built to give the French as difficult time as they gave the British in San Fiorenzo.

This answer, unlike the others, is basically based on a military architecture style change, and not on a detailed technological study of the military pros and cons. It is commonplace for people to make clothing style choices based on non-technological considerations: I wear a trench coat not because the straps and buckles are actually useful to me, but because Humphrey Bogart wore one, and I want to be cool like him. For the same reason there were Zouave regiments in the American Civil war, and a great profusion of different kinds of special military hats in the 19th century. (Such as illustrated here.) In the case at hand I suspect that the British decision to build Martello towers was in part born of a desire to be fierce like the defenders of San Fiorenzo, and by building forts as they did this desire was manifested concretely.

  • I actually mention some of this detail in my comment at the top. Nonetheless, I feel I need to point out that in my original question, I never doubted the effectiveness of the tower in itself, I was much more perplexed as to how a mere 103 of them could be expected to defend such a huge length of coastline, given that their effective ranges did not overlap. – Lefty Jul 11 at 6:37
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Another consideration is that if you land and advance along a narrow corridor between two towers you now made your invasion force very vulnerable to flanking attacks.

A small holding force can delay your advance along the corridor, and larger strike forces sneak up along your flanks and hit you from both sides and possibly the back as well.

As a result such a tactic is a disaster waiting to happen for any invading force, something jungle patrols in both WW2, Vietnam, and no doubt elsewhere experienced all too often.

Even worse, your entire supply train is now also limited to that narrow corridor, so even by just blocking that corridor the English could have simply starved you of supplies and then hunted you down at leasure.

And funneling all your ships into that narrow section of beach, and landing your supplies there as well for the duration, leaves your fleet vulnerable to a concentrated attack by the English home fleet, coming in from both sides as well, crushing your ships between two flotillas.

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I would like to add to some of the excellent answers here. Small land based fortifications could be extremely effective against ships because they can use heated shot.

In a stone fortress you can heat case shot to red hot before firing this would set wooden warships on fire, a huge hazard for these vessels. The vessel could not reply in kind, having the furnace aboard to heat shot would be a fire hazard in itself, and heated shot is no more effective than normal shot against a stone fort.

  • Really interesting. The shot must have lost quite a lot of the heat whilst in transit, but I can see how it would have retained enough to still cause fires on wooden ships. – Lefty Jul 11 at 8:07
  • Wooden ships regularly would use fire arrows and things like that against each other. Braziers with burning coal were commonly used to cook food as well on board them. And as @Lefty says, the heated shot would cool down significantly in flight, you're far better off firing hollow balls filled with Greek fire or something else that's actively burning, with the container shattering on impact. – jwenting Jul 15 at 3:56
  • @jwenting Wikipedia is a strong source for this and I have spent a very long time studying Naval history. Please cite your source for Napoleonic warships using fire arrows in battle. Galley fires in this era were very carefully contained and controlled and certainly not an open Brazier, they were extinguished before battle. Greek fire was reputed to have been used further back in history but the presence of a self igniting chemical on wooden ships doing long sea passages would be hazardous in the extreme. – RoyC Jul 15 at 7:43
  • They were used extensively in the classical era, at distances and trip durations no different from those encountered in the English channel. If they weren't used by the English and French of the time, that doesn't mean they could not be used. But as you said, against coastal fortifications they were pretty useless. – jwenting Jul 15 at 10:36

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