Navy chief says Defence Force must do better after young diver Zachary Yarwood killed in a training exercise

A Navy chief admits the Defence Force must do better following the death of a young diver killed in a training exercise.

The Defence Force was fined more than $288,000 in the Auckland District Court on Friday over Zachery Yarwood's death.

Yarwood was critically injured during the diving exercise in Devonport last year. The 23-year-old died in hospital a day after he was pulled from the water.

The judge said on Friday there should have been at least four supervisors at the training course, but there were only two.

Chief of Navy David Proctor has apologised to the family.

"We take safety very seriously in the Defence Force - whether it be Army, Navy, or Air Force," he said.

The Defence Force must improve its practices to avoid fatalities during training exercises, Proctor said, and Yarwood's death was tragic.

"The loss of a sailor under training is never acceptable."

Proctor said nothing he can do will bring Yarwood back, but has promised to make improvements.

"We work very very hard to ensure we have the right processes and practises in place.

"What happened here was not okay - we must do better."

Yarwood's family, however, has not accepted the apology and say the Navy ruined their lives.

His mother, Elizabeth Yarwood, told the Auckland District Court on Friday she has recurring dreams of her son at the bottom of the sea.