How Has Anti-submarine Warfare Improved

WWII Submarines have deck guns. How were they protected from being submerged in salt water?

The barrels were protected by a waterproof plug that had to be removed before firing. The breaches were gas-tight for firing and so were water-tight as well. The metal was protected by the same primer and paint that protected the hull of the sub and of course everything that might freeze up due to rust was liberally lubricated and frequently inspected.Early in the war the German U-boats would often surface and fire on merchant ships with their deck guns, giving the sailors the option of disembarking into life boats before they sank the ship. Later, when convoys were were common and the danger from escorts or aircraft was omnipresent, this tactic fell out of favor.As far as I know, with improvements in anti-submarine warfare on all sides, the use of deck guns became increasingly rare.

How many submarines would Germany have needed to make a difference in the second world war?

Dönitz reckoned he needed 300 from a very early date. When the war started, he only had 26. If he had been able to start with 300, the results might well have been very different. It might have created a successful blockade that would have forced an early UK surrender. In the early days, U-boat detection was very poor. The blockade nearly succeeded much later. However, manufacturing such a fleet would have been difficult to keep secret, and would have altered British response. History is a dynamic process…change one bit, and all of the other parts move around.From: U-boat Operations:Chief of U-boats Karl Dönitz estimated he needed 300 U-boats to defeat the Allied convoys and force Britain into submission. When war broke out on 3 Sept 1939 he had 26 ocean going U-boats. The 300 U-boat figure was calculated by him to mean that from this figure 100 boats would be in repairs, rest and working-up, 100 more on their way to and from operational areas - leaving on average 100 U-boats in actual combat areas. This meant about 200 U-boats would have been at sea at any one time, but with the French and Norwegian bases resulting in shorter transit times the ideal figure would be somewhat lower.On 8 Aug 1942, nearly 3 years after the war began, the number of U-boats at sea reached 100 for the first time (some of these boats were inbound or outbound from bases). Dönitz finally had much of the striking power he had been insisting on.For the next 11 months the number rarely dipped below 100, reaching as high as 159 on 29 April 1943. That peak was just in time for the horrific losses during May 1943 when 41 U-boats were lost to steadily improved Allied anti-submarine warfare.

How good would modern submarines be at unrestricted submarine warfare?

The first week of unrestricted submarine warfare would be pure hell for maritime commerce.  Modern boats are hard to detect and fire weapons that nearly never miss.  Then two critical events will occur.  Maritime commerce will make it into the nearest safe port, and the submarines will run short of weapons.Let's look at the second event first.  Once you're out of weapons you're going to have to reload.  Reloading will only occur in port; weapons reloads can never occur at sea, it's just too risky.  Depending on who the belligerents are those ports will most likely be interdicted, meaning someone, somehow is going to put that port out of action, either by blowing smoking holes into the port, or by sinking all vessels trying to enter the port.  Even submarines have to surface to enter a port.  An interdicted port is not a useful port.As for the first event, maritime commerce sitting in safe ports are useless until they are escorted.  The easiest way to escort merchantmen is via the convoy system.  Convoys are very effective at getting lots of commerce ships through with minimal loss and maximum damage to attacking submarines.Now having said all this, none of this matters because we really haven't asked the right question; Why is a nation conducting unrestricted submarine warfare?  This is important because it goes to the war aims of the belligerent nation.  Is this nation trying to hurt another nation economically?  Then submarines may only be part of a more complete blockade solution.  Is the nation trying to defend itself from a larger more powerful nation?  Unrestricted submarine warfare may be the only tool that the smaller nation has to hurt the larger nation, a kind of asymmetric attack at sea.  The context is even more important than the capability because it gives the why of the war, which in turn tells you what the aim of the belligerents are.Is unrestricted submarine warfare even a viable strategy in this modern time.  Certainly, if it can be sustained.  But very few nations have the ability to sustain that kind of warfare for more than a week.  It would entail being able to defend your submarine logistics points and being able to defend against an enemies convoys.  You can count how many nations in the world have that capability on one hand.