No. Washington is one of the 37 states that allow unlicensed civilians to own silencers, but the only one of those states that bans their use by anyone, police and military included. Bill 5112 makes an exception for silencers that are registered with the federal government.
The police (for the most part) want this bill passed. They like to use them for the same reasons civilians do. Thousands of people own silencer in WA. It is just that their use had been banned since 1934, allegedly over poaching issues.