During WW2 submarines were widely utilised. Turkish Navy, founded in back in 1081 A.D. was among the 20 nations that had submarines in naval inventory during WW2. When we look at the submarine numbers of these countries:


Country - Commisioned submarine number
Germany - ~1200-1300
USA - ~300-350
Japan - ~250
USSR - ~200-250
Britain - ~150-200
Italy - ~140
France - ~100
Netherlands - ~25
Turkey - 13 (2 of 13 was withheld, so the actual number decreased to 11)
Poland - 9
Chile - 8
Finland - 5
Peru - 4
Greece - 2
Estonia - 2
Yugoslavia - 2
Norway - 2
Brasil - 1
Romania - 1
Australia - 1


Turkish sumbarines during WW2 and their classes.
Inönü Class (German Type UB III variant, ressembling early Type VII)
I. Inönü
II. Inönü
https://upload.wikimedia.org/wikipedia/commons/c/c5/Turkish_submarine_Birindji-In-Uni.jpg

Dumlup?nar (Italian Vettor Pisani Class)


Sakarya (Italian Argonauta Class, 600 Series)
https://upload.wikimedia.org/wikipedia/commons/b/bd/Turkish_submarine_Sakarya_DzKK.jpg

Gür (German Type IA variant)
https://upload.wikimedia.org/wikipedia/commons/5/5c/Turkish_submarine_Gur_1936.jpg

https://upload.wikimedia.org/wikipedia/commons/b/bc/U-boot_E-1.png

Ay Class (German Type IXA variant)
Sald?ray
Bat?ray (Withheld by Germany)
At?lay
Y?ld?ray
https://upload.wikimedia.org/wikipedia/commons/3/3e/Turkish_submarine_Atilay_DzKK.jpg

Oruç Reis Class(British S Class variant)
Burak
Murat
Oruç
Uluç Ali Reis (Withheld by Britain)
https://upload.wikimedia.org/wikipedia/commons/7/7b/Turkish_submarine_Burak_Reis_1946.jpg

https://upload.wikimedia.org/wikipedia/commons/8/80/Turkish_submarine_Murad_Reis_1942.jpg

https://upload.wikimedia.org/wikipedia/commons/e/e5/Turkish_submarine_Oruc_Reis_1942.jpg

https://upload.wikimedia.org/wikipedia/commons/b/b3/Turkish_submarine_Oruc_Reis_DzKK.jpg