During submerged test runs off Port Jefferson in Long Island Sound two weeks later, however, her crew discovered several leaks and the submersible docked at the Lake Company's marine railway for repairs and alterations.

Aside from a brief period alongside submarine tender Tonopah (ex-Nevada) to repair damaged screws in March, she spent the next five months conducting trial runs, dive tests and training operations out of New London.

Following another yard period at Bridgeport in mid-July to replace defective lube pumps, the boat moved to New York City on 30 August for final acceptance trials.

The latter included harbor net defense deployment drills with tender Fulton in June and stationary dives with a submarine rescue bell in the Thames River in September.

In late October, G-3 carried out instructional sound work with Parthenia, a task resumed in early 1918 in company with a succession of submarine chasers and patrol boats.

Resuming school duties on 17 July, G-3 spent the next three months conducting torpedo instruction, listening and radio training for officer and enlisted submarine students.