Some 339 officers with the Milwaukee Police Department will be eligible to retire by the end of 2017. That means nearly 20% of the city's 1,889 sworn police officers could retire over the next 18 months.

"It's certainly not a revelation," said Mike Crivello, president of the Milwaukee Police Association. "For years, I have been preaching to the Fire and Police Commission, the Common Council, and the mayor's office that this would happen."

Milwaukee Mayor Tom Barrett said the city has been closely tracking officer retirement numbers for years, and considers retirements when hiring new officers.

"We are well aware of the fact that there are going to be a significant number of people eligible for retirement, and that goes directly into our budget planning process," Barrett said.

The mayor said he anticipates the city will hire more new police officers to cover those retiring, but added that the total number of officers may not increase.

Sworn police are eligible to retire at age 57, or after 25 years of service, the Milwaukee Journal-Sentinel reports.