crash-dive 
verb [no object]
1(Of a submarine) dive rapidly and steeply to a deeper level in an emergency.If the submarine had come under attack, both men would have quickly drowned with no hope of escape as their boat crash-dived....
- Often, in the mid-Atlantic, after forcing U-boats to crash-dive, carrier planes dropped homing torpedoes on the submarines.
- Anyway, Brick's good piloting brought the sub back in view, now crash-diving to yet away.
1.1(Of an aircraft) plunge steeply downwards into a crash: pilots crash-dived on bridges over the Oder, destroying three of them
noun
(crash dive) A steep dive by a submarine or aircraft.‘There was a lot of noise and debris flying about and the helicopter went into a controlled crash dive but Pete had only partially detached himself,’ said Mr Dell....
- The man admitted that he had been playing with the helicopter and was making a crash dive move.
- Forty minutes later we make a crash dive, regrouping at 15m below the surface current that whips across the reef-top.