[Pants]

I dont think a Snorkel was EVER fitted to a IID, The only way to increase range was to install additional saddle tanks which were fitted to the sides of the external hull. These saddle tanks were used to accomodate additional diesel storage tanks. The diesel oil would float atop the saddle tanks and as the oil is consumed, sea water would gradually fill the tanks to compensate for the positive buoyancy. The range was nearly doubled to 3,450 nautical miles at 12 knots and enabled the Type II to operate around the British Isles. A further development was the propellers were fitted with Kurt nozzles, intended to improve propulsion efficiency.
And as for the AA it was only fitted with 20mm Twin Flak with only 1,000 rounds. It had Three 21 inch Torpedo Tubes, 1 reload ( total of 6 torps in all ) and could carry TMA, TMB mines.

A brief history on the Type II's......

Small and cramped, the Type II were coastal boats intended principally for training, but because of the shortage of available boats, they were later relegated to war duties. With a crew of 25, the boats had limited range and carried enough provisions for three to four weeks, but frequently returned to port after expending their supply of torpedoes.
Due to their small size and heavy rolling on the sea, the Type IIs quickly earned the nickname “Dugout Canoes”. Although of limited use in the open ocean, some remarkable successes were accomplished early in the war by U-boat aces such as Otto Kretschmer. The Type II also earned the respect and admiration of the crew due to its high maneuverability, rapid diving time and durability. Later in the war, due to the ever increasing need for training new crews, all Type II U-boats were withdrawn from combat duties and assigned to full-time training.
A total of 50 Type II U-boats were built during the war. There are four variants, Type IIA, IIB, IIC and IID.