'Tank' watches were technically products from WW1 experience of tank operators during that war. That's where the term came from. A lot of men used to tie their pocket watches to their wrists with leather bands, or made wrist bands to hold them in place.
Thing was, in the 1920's (and in many locations into the 30's) wrist watches were still looked upon in as being feminine in nature. One famous exchange between Federal court judge Kenesaw Mountain Landis and a lawyer appearing before him wearing a wrist watch happened in Illinois in 1922. That lawyer was told in no uncertain terms if he appeared before said judge wearing a wrist watch again, he would be found in contempt of court, heavily fined, and thrown in jail, as the judge considered pocket watches the proper attire for a professional to wear in HIS court room.
So, though popularity was building in the 30's for the wristie, and pocket watches were rapidly losing their position as being THE time piece on a person, it still held strong in many areas outside the larger cities. It wasn't until WW2 came along that the wrist watch really became the main timepiece worn by men, even though the pocket watch still held a strong position as THE navigation watch of the military.
What do I find ironic? Folks who say that pocket watches are 'passe', and yet they reach into their pocket to pull out a cell phone to check the time. True, a cell phone is a multiprocessor....but come on, in this case it's nothing but a glorified pocket watch.
Regards! Michaelson