Complex sentence: U- 515 fired at the plane with her 3.7cm anti-aircraft, the plane's bombs missed U- 515 and U- 515 failed to shoot down the plane, U- 515 again submerged.
Split into simpler sentences: U- 515 fired at the plane with her 3.7-cm anti-aircraft. The plane's bombs missed U- 515 and U- 515 failed to shoot down the plane, then again submerged.