"The move is in response to one of their colleagues undergoing treatment to change from a 42-year-old married man into a woman called Lauren.
But senior officers have said it constitutes "political correctness gone mad" to have staff on anti-discrimination training when they could be out on the beat.
A total of 510 staff - including 344 police officers - working for Humberside Police in North East Lincolnshire received a letter from the chief superintendent saying they had to attend the half-day training course to help PC Lauren's transition.
The training is likely to cost thousands of pounds but could help to protect the force from a potentially embarrassing lawsuit if PC Lauren were to experience discrimination.
Kevin Sharp explained in his letter that she suffered from gender identity dysphoria, which left her feeling like a woman trapped in a man's body.
"As from today, Lauren starts her new life and over the next few weeks you will receive awareness training during which you will be able to read a personal letter from Lauren," he said.
"I trust you will have the same determination as I have to help Lauren return to work with as little fear and trepidation as is possible. . . but feel much happier than she has ever done before."
He is not changing into anything but a man with feminine features. No operation in the world can convert a man into a genuine woman. Hillary Clinton, on the other hand, is proof positive that females can morph into males but thats another story.
Otherwise, I'm speechless.