A History of Research and a Review of Recent Developments

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The effects of explosive loading
350 kg of TNT, detonating 16 feet below the water line. This ripped a hole 20
ft by 18 ft and flooded damaged spaces with 1140 tons of seawater. The
second test was to detonate 100 kg of TNT near the relatively unprotected
bow and 12 feet below the waterline, and this ripped a hole 19.5 ft by 16.25
ft in the hull. A third test used 150 kg of TNT 20.8 ft below the waterline in
the area near the main gun magazines, producing a hole 19 ft by 17 ft. It is
interesting to note that the large variation in charge size did not produce a
noticeable variation in the size of the hole through the hull.
A further useful test was carried out on the Tosa, when a projectile with an
underwater trajectory was fired at the hull. The projectile was a 40 cm armourpiercing
shell, which struck the ship 11.7 ft below the waterline, as shown in
Figure 8.15. It penetrated the outer hull plate, the inner bottom plate and a
torpedo bulkhead (3 inch high tensile steel plate) before exploding. A section
14 ft by 8 ft was carved out of the double hull, and a total of 2950 tons of
seawater gained access to the damaged area. These tests have been recorded
in the History of Japanese Naval Construction, written in the 1950s by 50 of
Japan’s leading naval architects and naval constructors.
The structural response to explosions of submarines is another area where
much classified research has taken place. The resistance of hulls has been
increased, partly by the introduction of high-strength steels which lessened
the chances of hull splitting and flooding under attack by depth charges. It
was pointed out by Roseborough, also in the discussion of Kiel’s paper, that
damage to internal components and systems was more likely than hull damage.
Such damage could make vital controls inoperative, causing the submarine to
exceed the hull collapse depth or conversely to surface out of control. The
need to preserve the integrity of seawater systems within submarines, and
their hull valves, in the face of explosions was also underlined by Roseborough.
A submarine hull is often a ring stiffened cylinder, which lends itself to an
analytical as well as an experimental evaluation of structural performance, so
Figure 8.15 Tosa armour-piercing shell experiment (from Keil, ref. 8.31).