Louis Meulstee has a fascinating article on the Gibson Girl Rescue Radio transmitters from World War II. So what's pinup have to do with an air/sea rescue radio? First a little background. Charles Gibson created an era's idea of the perfect woman- the "Gibson Girl" in the late nineteen and early twentieth century. She was known for her hair being piled upon her head, and an "S" shape enhanced with a tight corset. Camille Clifford is probably the best known model of the era. Many models followed, including movie stars- yet they all had those curves in common.
The US manufactured an emergency transmitter type AN/CRT3. It was quickly nicknamed the 'Gibson Girl'. Based on a German design, it was basically a box with a crank on top to run a generator. Pretty clever idea- you never have to worry about dead batteries. Speaking of clever, the Americans and the British had a few tricks up their sleeves on how to get an antenna up in the air as well. You had your basic box kite- or even rockets to get the kite up there. If that didn't work, there were balloons included- which when coupled with a kit mixed with seawater lifted the antenna skyward. So back to the transmitter itself. Since you had to hold it between your legs to crank it up, it has an hour glass figure of its own, hence the nickname and it's association with pinup. You can read the full story about the radio here, and a little on Gibson Girls here.