Past perfect - Return to Titanic

When Titanic hit the iceberg it was / had been at sea for five days.

By the time a rescue boat came, many people died / had died.

When Ballard used video technology, he found / had found the wreck.

Ballard wanted to return to the wreck to see how it changed / had changed.

By the time Ballard returned to the site, several people visited / had visited it.

When Titanic hit the iceberg, it sank / it had sunk.

By the time they sounded the ship's alarm, it was / had been too late.

Many ships sunk / had sunk in the same area where Titanic was found.