Story highlights More than a third of warfare training certifications for the Navy's Japan-based destroyers and cruisers had expired in June

There are 70 to 80 ships and submarines in the 7th fleet

(CNN) A government watchdog is raising new concerns about the safety and readiness of US ships in the Pacific region following a series of collisions that led to the deaths of US sailors.

More than a third of warfare training certifications for the Navy's Japan-based destroyers and cruisers had expired in June -- a five-fold increase from two years prior, the Government Accountability Office has found.

In testimony to be delivered Thursday, the GAO found that 37% of the Navy's destroyers and cruisers in Japan had expired -- up from 7% in January 2015 -- and over two-thirds had been expired for five months or more.

The GAO testimony, a copy of which was obtained by CNN, will fuel new questions on Capitol Hill about the cause of the four Navy ship collisions in the Pacific this year, in which 17 sailors were killed, and the health of the Navy fleet.

After the USS John S. McCain collided with a merchant vessel last month off the coast of Singapore -- an incident that accounted for 10 of the 17 deaths -- the commander of the 7th Fleet was dismissed, and the Navy ordered a rare, one-day operational pause for its entire fleet.

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