[Jaystew]

I think for me when I'm on the open ocean I don't bother checking the hydrophone as often as I should. But in the early war it is definitely worth checking when going through a 75-50km chokepoint rather than doing a visual sweep because you can cover so much greater area. I also dont think its a bad idea to do it every 2-4 hours while on patrol or in a high risk area.

Knowing that there is a contact to the south when it could only likely be an escort patrol such as in the shallow waters or near a port, definitely helps make good navigation decisions and avoid the enemy. Once in visual range its sometimes hard to get out of a slow sticky situation with escorts. Especially in shallow shallow shallow water!

As the war goes on it becomes more and more important as surface travel is either limited, dangerous or almost impossible. More destroyers and aircraft in 1940 make for minor irritants to surface travel, in 1941 especially after the USA enters the war it becomes even more limited. In 1942 I think its dangerous to be on the surface not just during during the midday but even at night. In 1943 with all the aircraft if you get spotted or detected by their radar they will relay your position and if you are not in deep water the destroyers will ASDIC you to death and DC you and use hedge hogs boom boom boom. Not only in 42/43 do you not have the advantage but even with the schnorkel until the Type XXI in late 44/45 does the Kriegsmarine have the advantage again and at that point the war is already lost.