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I'm interested in knowing how the guns' holes in battleships' turrets protected, if and when they were, and how was that protection designed and arranged, specially in relation to the guns' elevation axis.

In tanks, the turrets' holes that fit the main guns are protected by "gun mantlets", which are designed and fit in a manner where they "completely" cover the turret holes even in different gun-elevations.

But they are usually designed in a manner that is external or contiguous to the shape of the tank's turret, and that keeps the mantlet very close to the gun's elevation axis:

  1. A close-up to a Tiger's external-style mantlet.

enter image description here

  1. A close-up to a IS-2's blend-style mantlet.

enter image description here

However, for large-caliber naval guns, the size of the guns, the thickness of the turrets' face armor, and the much greater gun-elevation angle requirements, impose great limits to turret-design; with most turrets for guns of calibers including and above 12" being made plain and boxy; usually having a straight face plate, and apparently either no mantlet at all, or with internal mantlets that would leave considerable gaps open, depending on the elevation of the gun.

In particular, I'm interested in the design and arrangement of the mantlets of the main batteries of the Iowa-class battleship(s) and the Yamato's.

So far, my research has led me to few results, as photos featuring the turrets without their blast-bags over the gun-holes seem to be extremely rare, and photos of them still under assembly but with the guns already mounted being even rarer.

The few images I've found raise more questions than answers. The best images I have found are these:

  1. BB-61 Iowa, featuring the guns without blast-bags and in different elevations. Apparently there would be a huge gap below the guns if they were put to the maximum elevation of 45º. Also, from photos of the installation of 14-inch guns from other ships, it appears that mantlets were often of a much thinner thickness than the turret's face plates.

enter image description here

  1. Yamato, featuring what appears to be a circular mantlet that "digs" into the turret's face-plate from the back. The elevation axis are a mystery too, needing to be very close to the face-plate to allow the mantlet to completely cover the hole within the face-plate's thickness without leaving neither protrusions nor gaps, despite the plate's angle; and yet, that seems unlikely to be the case. enter image description here

EDIT: Note - As soon as I have the time, the question will be revised and formatted to use proper technical terms, which I learned through the sources that acquired through the research efforts, both of my own and from others here.

This will be done to increase clarity for "archiving" purposes, so that other people with the same interest will have a higher chance of understanding the terminology, and therefore the question, the discussions in the comments, and the answers.

As always, the StackExchange community was great regarding both the effort everyone put into helping to solve the questions, and the etiquette displayed.

I would like to thank all participants of the discussions and answers for my question, who dedicated some of their time and will to help me understand a little more about the principles that guided this aspect of WW2 warship armors; and I want to specially mention Conrad Turner, Kentaro Tomono, CGCampbell, jjack and jwenting, for their distinguished efforts.

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  • As your examples show, the exact solution would vary depending on the chosen turret so there's going to be as many different answers as there are different turret designs.
    – Steve Bird
    May 24, 2015 at 8:49
  • It seems to me I can only answer about Yamato ( though still tough due to the exsience of many technical terms ). If it is O.K then, I will answer. I can not cover for Iowa class.
    – user12387
    May 24, 2015 at 15:54
  • @KentaroTomono Please do. Half an answer is better than no answer at all, and while ...
    – CosmicGiant
    May 24, 2015 at 16:04
  • Comments are not for extended discussion; this conversation has been moved to chat.
    – T.E.D. ♦
    Jun 1, 2015 at 12:42

3 Answers 3

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After some more research I stand by my earlier comment in general the gun ports had minimal protection, relying on small size and being in the shadow of the gun. There is a large amount of negative evidence for this, for example in his books Warrior to Dreadnought, The Grand Fleet and Nelson to Vanguard D. K. Brown does not mention protection to turret gun ports.

The positive evidence I cite the cross section of a 14" three gun turret on Eugene Solver's US Navy pages which shows no protection to the gun port. From the same site we have access to OP 769 Configuration of the Three Gun Turrets of the USS New Jersey which explains that there are upper and lower shield plates on the gun slide. These do not seal the gun port and at best provide protection from 6" projectiles and splinters. The arragements are shown in the accompanying illustration, from which their thickness can be measured which when compared to the face plate thickness is equivalent to about 3" thick. The relevant section of this document is shown below:

enter image description here

Further research turns up this entry on the NavWeaps site

Gun Port Shield - Curved armor plate attached to a gun barrel such that it seals the gun port in the glacis plate, regardless of the elevation of the gun. Gun ports are by their very nature weak points in the armor protection of a gun mounting or turret. Gun shields seal these openings and are intended to provide at least some measure of protection from shell splinters. In addition, many gun shields are designed so as to keep water and weather out of the interior of the mounting or turret. Some images of gun shields may be seen in these photographs of a USN 6"/47DP and a German 38 cm SK C/34.

A rough estimate of the gun shield thickness in this photo (reproduced below) can be made which is very roughly ~4" (maybe a bit more?).

The Yamato's gun shield appears to be similar in form to that of the German 38cm (15") gun shown.

enter image description here

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  • Although I found the navweaps link first (see my comment to jwenting's answer), you are providing enough evidence from different sources to allow at least for basic cross-checking. I will keep researching on my own, but for now, this seems to be the most complete and the most reliable answer, so I will mark as accepted.
    – CosmicGiant
    May 25, 2015 at 14:23
  • I should point out that the NavWeaps definition of "Gun Port Shield" should be taken as indicative rather than definitive since as we have seen with the New Jersey turret section diagram the shield is not necessarily curved and it does not seal the gun port in the front plates of the gun house.
    – Conrad Turner
    May 30, 2015 at 6:55
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Telling from your pictures of the Yamato and an Iowa-class, the holes were covered from the inside using steel, probably with less thickness than the turret armament. The combat environment of tanks and battleships is different, with battleships receiving more fire from higher elevation angles than tanks. This leaves mostly shrapnel from the deck as a threat to the interior of the turret.

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  • If that is the case, why were the turrets' face-plates angled backwards? Specially in the newer ships like the Iowa-class and the Yamato-class, which seem to be angled at or near 45º. That would make the face-plates align with the incoming shells' vector, and decrease their effective thickness. --- Also, supposing a hit from an opposing BB firing with maximum elevation of 45º, the incoming shells were guaranteed to fall at angles steeper than 45º, and so why is the turrets' top armor (Iowa = 7.25in) considerably thinner than the face-plate (Iowa = 17in)?
    – CosmicGiant
    May 24, 2015 at 14:55
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    If the face plates were not angled backwards, but straight for example and covering the hole completely, the barrel couldn't turn up or down. The backward-angled face plate is a must for being able to change the barrel's elevation angle. 45° is probably the barrel elevation for maximum range, but the effective thickness of the top armor is still 7.25in/sin (45° × pi/180°) = 10.25in. And that is at max, range. The closer the other ship, the flatter the trajectory of its projectiles. The flatter the trajectory, the larger the effective thickness of the top armor.
    – jjack
    May 24, 2015 at 17:11
  • "If the face plates were not angled backwards (...) the barrel couldn't turn up or down" - I highly doubt that, as the elevation of the guns was dependent on the holes made for them in the face and top plates of the turrets, rather than in the angle of the plates themselves. This is exemplified by the fact that most German, UK and USSR (Russian) battleships and dreadnoughts had flat or considerably less-angled face-plates, like, respectively, the Bismarck-class (flat), the King George V-class (flat), and the Sovetsky Soyuz-class (60º rather than 45º).
    – CosmicGiant
    May 24, 2015 at 17:58
  • Pictures of detailed turret models available on the web show Bismarck to have round plates. If you have a flat plate as a fixed shield around a gun barrel, perpendicular to it, and you move the barrel up the shield goes with it. The bottom of the shield gets pushed against the front armor of the turret.
    – jjack
    May 24, 2015 at 18:20
  • The "face" plate refers to the turret's "fixed" front armor. It's not fixed to the gun barrel, and does not move with it. The armor that is fixed to the barrel is, at least in tanks, referred to as the "mantlet", and unless it is external, yes, at least internally it's designed round and with it's diameter centered on the elevation axis, so as to not conflict with the turret during gun-elevation; But this has little, if anything, to do with the turret's face-plate, including the face-plate's angle.
    – CosmicGiant
    May 24, 2015 at 18:59
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One factor not mentioned in the other answers is this:
Those openings are very small relative to both the size of the vehicle and the accuracy at engagement ranges of the weapons trained against it.
In other words, chances of the openings being hit are very small indeed, even if deliberately aimed for.
Hence they're typically either unarmoured or armoured against small arms (rifles, machine guns) fire only, their size being their main source of protection. A canvas sheet as seen on the guns of ships provides protection against water getting into the ship in rough seas or rain/snow conditions. Some land vehicles and even aircraft have similar sheets in place.

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  • Can you give any sources for the "chance of hit" argument? I just found one stating in favor of your argument, but I'd like more for cross-confirmation. (Source; see "Gun Port Shield": navweaps.com/Weapons/Gun_Data.htm) --- Also, the canvases on the gun ports of battleships (and other large caliber guns) are called blast bags, because although they also protect from the "natural environment", their main purpose is to prevent damage to equipment and/or crew from the guns' firing blasts, which, for the Iowa, could seriously injure within 15m, and still have adverse effects further.
    – CosmicGiant
    May 25, 2015 at 4:13
  • @TheLima general knowledge about accuracy of WW2 weapons I've picked up over the decades... E.g. a tank (depending on type and crew skill obviously) would be lucky to hit another tank at more than a thousand meters or so. To hit a target a few square centimeters in size on that tank with a shot specifically aimed at that spot would be nothing short of a miracle unless you were suicidally close
    – jwenting
    May 25, 2015 at 4:22
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    The chance of hit argument essentially reduces to the argument that the ratio of the hole area to the area of the turret front is a small number. This small number says that it is very unlikely that this opening is hit.
    – jjack
    May 25, 2015 at 10:55
  • jwenting & @jjack I understand the argument guys, but I still need at least one more source in order to cross-confirm. You should know that the internet is full of misinformation and, while I don't believe this is the case here, "I want to believe as many true things, and as few false things, as possible" ( - Matt Dillahunty), and for that, I need to cross-confirm, and/or peer-review my sources whenever possible, which I think is the case here. I don't intend to sound doubtful of your claim, but: You've picked up knowledge over the years? Good! Tell me where some of it came from!
    – CosmicGiant
    May 25, 2015 at 14:04
  • Merely by thinking about it, really.
    – jjack
    May 25, 2015 at 19:39

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