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Thanks to StrategyPage we have the book review from Professor Al Nofi.
American submarines operating on the surface quite often eschewing the use of torpedoes and employing the deck gun to sink an enemy vessel.
"Surface and Destroy: The Submarine Gun War in the Pacific", by Michael Sturma
"Although not really what one thinks of when discussing submarine operations [as during the Second World War], surface gunnery actions are occasionally mentioned in naval histories [of the Second World War], and in this work Prof. Sturma (Murdoch, Australia), demonstrates that they were in fact not at all uncommon."
"Calculating that there were literally hundreds of surface actions by Allied submarines during the Pacific War, Sturma, author of several earlier works on undersea warfare, examines a substantial number of them. While some of these clashes occurred because a submarine found itself unable to submerge upon the sudden appearance of enemy warships, most involved attacks on small vessels such as trawlers, barges, and sampans, during blockade operations. Other clashes took place because Allied submariners were engaged in rescuing downed airmen, or were trying to capture or inflict vengeance on Japanese seamen"
NOT using torpedoes but on the most dangerous or important of enemy vessels, the submariner if possible not cracking the egg with the sledgehammer, using appropriate means on the appropriate target.
That American Gato class submarine armed in such a manner to allow for formidable naval deck gun fire if and when the situation either demanded or for whatever reason was the preferred means of attack.
Deck gun weaponry of the Gato to include:
* 1 × 3-inch (76 mm) / 50 caliber deck gun.
* Bofors 40 mm .
* Oerlikon 20 mm cannon .
During the Great War [WW1] it being much more common for the German U-boat commander to sink enemy merchant vessels using his deck gun that expending a torpedo.
That number one ace of all ace submariners [and will always will be] Kptlt. Lothar von Arnauld de la Perière [Highest scoring U-boat commander of all time with 193 ships sunk for over 450,000 tons sunk] a predominant amount of the time the deck gun the weapon of choice!
"in April/May 1916 he sank 23 ships, totaling 68,000 tons on a five week patrol and in July/August 1916 in four weeks he sank 54 ships, totaling 91,150 tons using only 4 torpedoes (one miss). [using almost exclusively his 88 mm deck gun]"
P.S. Caliber of the deck gun that ratio of the length of the barrel to the diameter of the bore. The greater the ratio the more accurate the gun is considered to be!