After officially joining the Navy’s ranks, about 40 percent of the 40,000 sailors minted here each year remain at Great Lakes for specialized training, a period in which the young sailors have their first free time and get their first real salaries — and reports of sexual assault rise sharply.

Alcohol fuels assault, so young sailors are taught the warning signs for when a shipmate is drinking too much, and how to judge whether another sailor’s advances might be all about taking advantage. Hours of training focus on how to intervene gently but firmly to separate someone from a possible predator.

“Bystander intervention isn’t some grandiose thing, a knight in shining armor to keep someone from being raped,” said Petty Officer Corryn Fraser, a member of the base’s new peer-to-peer mentoring program. “It’s more: ‘Hey, you shouldn’t talk to her that way. That’s inappropriate.’ Or, ‘Don’t you think you’ve had enough to drink?’ ”

Although alcohol is served to those 21 and older at pubs on the grounds of naval stations in the United States and around the world, bartenders at Great Lakes are now prohibited from selling more than one drink at a time to any one sailor, and buying a round for several friends is also no longer allowed. Each sailor must line up, and show ID, to pick up a drink.

Some of the assault-prevention initiatives are conducted by specially trained Navy personnel, and some by academic experts or social workers who charge only for travel expenses. Other advanced sessions — one is called “Sex Signals” and another “Afterburner” — are taught on contract and cost the Navy about $500,000 a year. The sessions include a video depicting a fictionalized rape, supplemented by lengthy discussion, which can get explicit.

The Navy acknowledges that it cannot use training to change the behavior of sexual predators, but it is trying to train the rest of the sailors to watch out for one another.

Another new initiative replicates the overseas “shore patrols” that keep watch for sailors taking too many liberties at ports-of-call around the world. Capt. Henry P. Roux Jr., the training commander here, dispatches naval criminal investigators in civilian clothes on “town patrols” along the coastline of Lake Michigan. Their beats include nearby railway stations, bus depots, taxi stands, pubs and clubs.