[Aktungbby]

https://www.uboataces.com/uboat-type-ii.shtml

The Type IIA was a single hull, all welded boat with internal ballast tanks. Compared to the other variants, it had a smaller bridge and could carry the German G7a, G7e torpedoes as well as TM-type torpedo mines. There was a single periscope in the conning tower with serrated net cutters in the bow.

IIC:The Type IIC was a further lengthened version of the Type IIB with an additional two compartments inserted amidships to accomodate improved radio room facilities and a second periscope. The additional diesel tanks beneath the control room was further enlarged, extending the range to 1,900 nautical miles at 12 knots.

U-57 TYPE II-C https://en.wikipedia.org/wiki/German_submarine_U-57_(1938) THERE WERE 8 BOATS OF THIS TYPE AND EVERY ONE OF THEM SANK A WHOLE LOTTA SOMETHING! U-57 SANK 13 VESSELS AND DAMAGED TWO
Summary of raiding history

Date Ship Nationality Tonnage: 17 November 1939 Kaunas Lithuania 1,566 Sunk 19 November 1939 Stanbrook United Kingdom 1,383 Sunk 13 December 1939 Mina Estonia 1,173 Sunk 20 January 1940 Miranda Norway 1,328 Sunk 26 January 1940 HMS Durham Castle Royal Navy 8,240 Sunk (mine) 14 February 1940 Gretafield United Kingdom 10,191 Total loss 21 February 1940 Loch Maddy United Kingdom 4,996 Damaged 25 March 1940 Daghestan United Kingdom 5,742 Sunk 17 July 1940 Manipur United Kingdom 8,652 Sunk 17 July 1940 O.A. Brodin Sweden 1,960 Sunk 3 August 1940 Atos Sweden 2,161 Sunk 24 August 1940 Cumberland United Kingdom 10,939 Sunk 24 August 1940 Havildar United Kingdom 5,407 Damaged 24 August 1940 Saint Dunstan United Kingdom 5,681 Sunk 25 August 1940 Pecten United Kingdom 7,468 Sunk NOTE:

Originally Posted by SAILOR STEVE

it looks like the rear tube is the attack periscope. Some photographs show a raised fixed housing in the rear, and the plan seems to show that as well. It also looks as if the viewing positions of both 'scopes are in the control room, not the conning tower.

I TRIED TO FIND A BLUEPRINT BUT IN LOOKING CLOSELY AT YOUR PLAN, I ALSO THINK THE ATTACK SCOPE IS USED IN THE CONTROL ROOM BUT IS THE FRONT (SMALLER HEAD LESS WAKE?) SCOPE...