One more uboat was fitted with a Schnorchel: U237.

In U.K.National Archives DEFE3-series of records with translated decyphered Kriegsmarine radio messages, there is message ZTPG 291773 (out of DEFE3/467) from Oct.3, 1944, wherin "Control" tells U237 to do "Schnorchel" training on Oct. 4.

Ritschel in his "Kurzfassung Kriegstagebücher deutscher U-Boote 1939-1945", vol.6, U237, mentions "Erprobung des 2.eingebauten Schnorchels" after Sep.1, 1944, which seems to imply that a 1st Schnorchel had been fitted even before this date.

E.Rössler in his "U-Boot Schnorchel: Entwicklung und Einsatz 1943-1945" (Verlagshaus M&M, Item 41 in the series on Germany's history, A5 format, 30 pages) also describes - and illustrates with a photo - that U237 was fitted with a Schnorchel.

Regards,
Walter