When were the 40mm guns first used?
 

Norman Friedman's U.S. Submarines Through 1945 says they were first installed in the fall of 1944, but in-game we can get them from the summer of 1943. Which one is correct?

Can't say for sure when they were first installed on submarines, but the Navy began mass-installing them on surface ships in early 1942 as a matter of course to replace the inadequate prewar 1.1 inch AA guns. Wouldn't be surprised if they were filtering their way down to submarines by 1943.

I tried them out a few times and wasn't overly impressed. I prefer having two twin 20mm guns. They throw a lot more lead into the air. :)

Staying on topic...

This is what Friedman says in the above book, on page 219:

Now, Friedman is known for being very accurate in his work, and I've never seen any references to 40 mm-armed boats before 1944. Can anyone add anything to this?

It could have been when they started early trials with it?? I'm not sure and have no way of checking (most of my reference books are still boxed up from my move!:cry:)

There is, of course, the possibility that some submariners outfitted their boats with 40mm's without it being an official modification. We are not talking about a section of the Navy known for waiting for permission to use new toys it gets it's hands on.

That wouldn't surprise me. There were a few US infantry units in France that had unofficial tank platoons attached. It's amazing what can be pilfered sometimes. ;)

This might seem like a strange reference source, but the strategic-level game War in the Pacific has a rather extensive naval database and has been pretty throughly modded and vetted by Pacific War enthusiasts since it came out 4 years ago. According to it the Gato Class is eligible for upgrade to a 40mm gun starting in June of 1943 assuming it's at a major port.

http://neptoon.homestead.com/WITPDataBase.jpg

Interesting data, there, Torplexed. It might just be that the 40mm really was available from that date.