Then Ab sank.
For just an instant Dalzell thought Canty had gone below on purpose.

Dan swam closer, to be of assistance.

Then he saw the bubbles of air coming up rapidly.
"Cantys given out--he's going to drown!" gasped Midshipman Dan, with horror.
Like a flash Dan dived below, found and clutched at Canty.

The young man returned the grip with interest, but Midshipman Dalzell struggled to the surface with him.

Ab Canty was exhausted, out of his head and altogether past reasoning.