Submarine School Completion Badge (beware--replicas are quite plentiful and fairly well-made).
Instituted on September 8, 1911 (Meiji 44)
Name change on April 14, 1919. (Taisho 8)
'Submersible' will change to 'Submarine.'
In Japanese (潜水艇sensuitei to 潜水艦sensuikan)
2nd name change on September 7, 1920 (Taisho 9)
Submarine Completion Badge to Underwater Academy Practice Student Completion Badge
潜水艦修業章Sensuikan shuugyoushou to 潜水学校練習生修業章Sensuigakkou renshuusei shuugyoushou.
Badge discontinued on July 25, 1944 (Showa 19)
Below are two replicas. Observe the difference in patina.
Hollow back. Late war?