Which upgrades for the uboot during a carrer are usefull, which ones are not?

[Aktungbby]

The best upgrade imho is the Zaukönig (5700 meters at a speed of 24 knots) EELS-bar none! The original FALKE (20 knots for 7500 m and was introduced in March 1943). is a tad slow; reality is such that once acquired it is a true 'fire and forget' weapon leaving u, the u-boot kaleun, to focus on evading the ever-improving anti-sub measures. The deck gun is fun but not as productive in a tonnage war. Use only to dispatch cripples. Have a few long range steam eels too. As for KDB: in reality, from British captured crew interviews, most of the Uboats reverted back to GHC after having un-installed KDB.

The initial impact of the acoustic torpedo in the Battle of the Atlantic prior to the widespread deployment of counter-measures cannot be overstated. The U-boats now had an effective "fire and forget" weapon capable of homing-in on attacking escorts and merchant ships and doing so in close quarters of only three or four hundred yards. By Summer of 1943, the German U-boat campaign was experiencing severe setbacks in the face of massive anti-submarine efforts integrating Coastal Command attacks in the Bay of Biscay, the deployment of merchant aircraft carriers in convoys, new anti-submarine technologies such as hedgehog and improved radar, and the use of dedicated hunter-killer escort groups. The Allies' improved escorts had greater range, and the use of fuelling at sea added hundreds of miles to the escort groups' radius of action. From June through August, 1943 the number of merchant ships sunk in the Atlantic was almost insignificant, while the number of U-boat kills rose dramatically and caused a general withdrawal from battle as the submarines could hardly make it through the Bay of Biscay to engage the convoys. For a time, the acoustic torpedo again put the escorts and convoys on the defensive...

[THEBERBSTER]

There is no deck gun upgrade in TWOS.
Two twin flak guns certainly raise the confidence level when on the surface.
Peter