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A question was recently asked about how Britain would have defended herself against a cross-channel invasion by Hitler. A key element in the British defense would be the Royal Navy. At the beginning of the war, it included (among other ships), something like 15 battleships and battle cruisers, 66 cruisers, and 184 destroyers.

One of the main concerns of the British army was that it had lost most of its artillery, and other heavy equipment at Dunkirk.

The Navy's first priority was to sink the German landing ships and covering naval forces. After fulfilling this assignment, the Navy could have been used as "artillery" to bombard (surviving) German land forces. If the above-mentioned ships were performing this "bombardment" role, how valuable would such support be?

Put another way, how much "artillery," or "firepower," would the Royal Navy represent (in batteries, divisions, or whatever other equivalent units of firepower might exist)? And if were being fired from the sea side, so that German ground forces were caught in a "cross fire" between British land forces and naval firepower, would such firepower be more or less effective than an equivalent amount of artillery supporting British troops from the land side?

  • It's worth noting that the Germans would not have invaded without air superiority, which is what the Battle of Britain was originally about. With German air superiority over the Channel, the Royal Navy would have been extremely vulnerable to air attack. Had they tried to oppose the landings by sea, their loses would have been very heavy. – Schwern Mar 4 '15 at 4:37
  • Another thing worth noticing is that not all British ships were present to protect the island. Some were on active convoy service, others were stationed in the Mediterranean or the far east. Not all ships would have been available for the defence of britain. – User999999 Jun 29 '16 at 6:56
  • @User999999: All ships "could" have been available for the defense of Britain, in a "last ditch" stand. It's like asking,"how large was the British army?" even though some of it would have been defending Gibraltar, Hong Kong, Singapore, etc. – Tom Au Jun 29 '16 at 14:27
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The land-based regiments would have a lot more firepower. Typically you might be talking several divisions having perhaps 2000+ guns combined. Note however these are relatively small caliber compared to naval guns. Most field artillery is 4-, 5- and 6-inch guns, whereas a battleship would have 8-10 15" guns.

The critical question in a fight like this is not so much firepower, as whether the invader can supply the beachhead. Soldiers need three basic things: water, food and ammunition. In mechanized warfare you also need lubricating oil and fuel. If a steady stream of these commodities does not reach the unit, they will surrender (or otherwise become ineffective). The importance of the navy would be to prevent supply ships, which are very vulnerable to any warship, from landing.

  • Upvoted. Even though your answer was "incomplete," it was hugely helpful in constructing my own answer. – Tom Au Oct 13 '14 at 13:34
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I was given several pieces of information in another answer that allowed me to construct my own.

First, I was reminded that the typical division of 10,000 to 12,000 men has about 2,000 artillerymen. At the rate of 20 men per gun, that is about 100 guns per division.

It was also helpful to learn that "most field artillery is 4-, 5- and 6-inch guns," because that's the caliber of destroyer or light cruiser guns.

If there were 66 cruisers (heavy and light), there might be eight guns per ship, or the total of about 500 six inch guns, or the equivalent. Each destroyer has about eight five inch guns, and 184 of them will have over 1400 guns. So far, we have enough guns for 19 divisions.

The 15 battlewagons would have about 8 guns apiece, or about 120 guns in total, but of much greater caliber than the field artillery. The radii of each of their shells would be about three times that of a destroyer, and their "throw weight" twenty-seven times that of the smaller shells, based on volume being 4/3 times pi times r cubed. (The first two terms, 4/3 and pi cancel out, so a battleship shell would be 27 times the size of a destroyer shell, based on 3r-cubed. Multiply this 27 factor by 120 guns, and you get the equivalent of over 3000 guns, or the firepower of about 30 divisions.

So Britain's naval artillery power was equivalent to that of 40-50 land divisions. And it would be probably be more valuable than an equivalent amount of land-based artillery because of the "crossfire" effect, and because it is easier to move this "artillery" by sea, than land artillery.

  • The crossfire effect is worth mentioning, as the psychological aspect of being bombed from both directions would be considerable. Especially as spotters and Royal Navy blindfire technology would allow shells hit German encampments even inland from the coast. – LateralFractal Oct 12 '14 at 23:51
  • and the greater mobility in coastal regions especially of naval guns. Faster to reposition a group of cruisers and DEs than a regiment of field artillery. The Royal Army had no self propelled howitzers at the time. – jwenting Oct 13 '14 at 2:25
  • two things to consider (1) spotting and co-ordination, naval ships were not as well co-ordinated I would have thought land based artillery with artillery observers trained for the job would be better (2) amount of ammunition carried on ships verese availability of shells on land. – pugsville Oct 13 '14 at 5:40
  • @pugsville Apparently the Royal Navy and US had radar and radio coordination of their shelling, whilst the Axis navies lacked this ability. RN ships could resupply at local ports and German ammunition would be limited to capacity of their own ships minus troops & vehicles. In practice RN's main purpose would be to cut the beachhead off from resupply. – LateralFractal Oct 13 '14 at 11:57
  • @LateralFractal: Fair enough. But it's comforting to know that the British navy had "50" divisions of artillery. As a practical matter, I would expect most of the navy to be destroyed interdicting the beachhead, and 20-25 divisions worth after the "mutually assured destruction" to help clean up what German infantry was left ashore. – Tom Au Oct 13 '14 at 13:44
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I have seen it stated that the British Navy would have been at the mercy of German bombers had the R.A.F. not contained them. Germany had a sufficient bomber force in September of 1940 to bomb day and night if required. However if the case of the Americans in the pacific, there was any amount of heavy bombers deployed against the navy of Japan. They proved notably ineffective due to the fact that bombes dropped from the combat operational height would only strike manoeuvring ship by pure accident.

  • I think you need to expand this to address the question more fully also you should include some references to your sources. – Steve Bird Jun 29 '16 at 8:21
  • The disposition of the R.N and capabilities regarding operation Sealion in 1940 is well presented in "Invasion 1940" Derek Robinson – Billmoore Jul 7 '16 at 10:33

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