@PotomacBobIn the USA armed forces I remember hearing VD / STD roughly equally in the 1980's. Medical personnel were more likely to say "STD" and the older NCO's were strictly "VD"
STI seems to have become more common in the 21st Century; although in the armed forces I heard STD more, and occasionally VD.
It seemed common for the armed forces to try to Scare the young men about the dangers of STD's and they Wanted to have a Stigma to them to hopefully reduce the incidents of STDs. However, if a soldier caught an STD, they would ensure they got treated, and tried to minimize any stigma...
I've read studies that the USA was particularly efficient at preventing VD during the Great War. In 1917/1918 the French and Commonwealth armed forces, or at least the ground forces in France had slightly more than 10% of their forces Suffering from the effects of VD. The USA forces in Europe, and the USA had fewer than 2%.
In WWII the USA was not able to isolate their forces in as draconian a manner as they had during the Great War. None-the-less, through various measures, including prophylactics, they still had fewer debilitating VD cases than most other nations.
It was not due to "superior morality" although certain cultural tendencies of a religious nature, and less tolerance for prostitution had some influence. Less occasions of rape were also a factor. Logistics and a superior abundance of medical care and medicines had more of an impact.
The USA is much more likely to punish members of the armed forces for rape or purchasing sex from a prostitute. Even in nations where prostitution is legal, in the 21st Century a member of the USA armed forces who Legally, in that nation(s), purchases sex, may still be prosecuted under the UCMJ for "Human Trafficking" and other Crimes! That started in the mid 1990's under the Clinton Administration.
None of these measures fully eliminated soldiers, sailors, etc. from buying sex from prostitutes, or other risky sexual activities, nor rape. However, it certainly seems to have reduced it at least statistically.
I have noticed a Drastic culture change! When I was first in, in the early 1980's, when Hay Street in Fayetteville, NC; near Fort Bragg, was the wild strip. Rick's Lounge, the Bunny Club, and the Lucky Saloon, were merely three of the more notorious dives in that "Wretched Hive of Scum and Villainy" (or perhaps Vice, instead of Villainy, although there were plenty of Villains there...)
In a similar vein, in several of my stories, since I choose to depict "unprotected" sex, I also mention testing for STDs. It isn't that complicated to test for STIs, nor does it take very long; at least if you use modern kits. Not "perfect" but good enough for a fictional story.