[flakmonkey]

Originally Posted by Dietrich

By way of comparison, the first Type-XXIII (Type-23, U-2324) was delivered from the shipyard on 17. July 1944 but did not sail on its first combat mission until 18. January 1945... the first of its type to go into service. It didn't contact the enemy until Feb'45. The Type-XXIII is a much simpler boat, smaller and with less complexity (although it was of the same genre as the XXI). Here's a timeline of its development:

21-Apr-1944 : Keel laid. Bauwerft Deutsche Werft AG.
16-Jun-1944 : Launched. Construction and fitting continues.
17-Jul-1944 : U-2324 Delivered
25-Jul-1944 : Acceptance tests completed and ownership transferred to the KM.
29-Jul-1944 : Buoyancy tests in the dock complete. Sailed (on surface only) to Kiel.
03-Aug-1944 : De-magnetisation complete. Sailed to Danzig.
07-Aug-1944 : Arrived at Danzig. Testing commences.
09-Aug-1944 : Minor damage incurred during testing is repaired.
10-Aug-1944 : Equipment overheats. More repairs required.
23-Aug-1944 : First "submerged mile test". Boat needed to surface halfway, due to failure of repairs
06-Sep-1944 : First testing complete. Sailed to Hela.
19-Sep-1944 : Dive plane testing.
21-Sep-1944 : Silent-running motor and propeller noise measured.
28-Sep-1944 : Periscope failure. Sailed to Holm-Werft in Danzig
01-Oct-1944 : New periscope fitted
03-Oct-1944 : U-2324 links up with U-2322 for attack practice
07-Oct-1944 : Due to hydrophone problems, practice aborted. Sent to 26.Flottille for repairs.
12-Oct-1944 : Sailed through the sea canal to Königsberg for hydrophone work.
mid-Oct-1944 : Return to 26. Flottille. Two days testing lost due to bad weather.
late-Oct-1944 : Tests complete. Testing crew depart. Combat crew arrive.
02-Nov-1944 : U-2324 sails for combat testing and outfitting.
04-Nov-1944 : Disrupted by heavy seas.
05-Nov-1944 : Diesel engine failure.
07-Nov-1944 : Arrives at Hamburg.
21-Nov-1944 : USAAF bombs Hamburg. Minor disruption to the shipyard, as only civilian targets were bombed. However, some delays incurred.
23-Nov-1944 : Additional outfitting.
late-Nov-1944 : Water influx into machine room at 9m deep. Fault was an incorrect;y built floor vent.
20-Dec-1944 : Repairs and tests completed.
21-Dec-1944 : Sailed to Tirpitzhafen for Schnorkel testing.
23-Dec-1944 : Schnorkel testing commences. During the first test, the connection cable of the FuMB-Dipole was broken.
25-Dec-1944 : Defective cable repaired.
early-Jan-1945 : Tarnmatte applied to Schnorkel.
09-Jan-1945 : Fitted with combat provisions.
18-Jan-1945 : Sailed for Norway on combat duties.
23-Jan-1945 : Arrived at Horten (Norway). Later sails to Kristiansand-Süd
31-Jan-1945 : Departs for operations area off the Scottish coast.
07-Feb-1945 : First contact with the enemy. No attack due to unfavourable position.
18-Feb-1945 : First attack against a coastal convoy, north east of Sunderland (England). Both torpedoes failed. U-2324 returns.
25-Feb-1945 : Arrives in Kristiansand-Süd.


I know that this is not a Type-XXI, which was the original topic of the thread, but perhaps it might give some ideas as to why it took so long to get the Type-XXI boats into service. The Type-XXI was far more complicated and had a larger crew and more equipment. There were more things to go wrong and, as has already been pointed out, they were a revolutionary (and hence unproven) design.

Even with the XXIIIs simpler construction the yards still struggled with the new designs, their biggest screw up with the typ23s was the shipyards estimated crush depth of 425m, in reality it turned out to be only 80m!