(I reposted this to correct a crucial typo in the title -- sorry!)
Not only were they contemporary figures, they were active members of the military or government. Churchill as PM, Mannerheim as Field Marshall, Weygand as Supreme Commander, etc.
The practice seems, to me, to have been pretty widespread, including the UK, France, Finland, and the USSR. When did this practice start, and when did it end? (Or did it even end? Though I have a hard time imagining the Boris Tank or the Biden-class aircraft carrier!)
More broadly, how were these things named? Was there a process, or did someone just, well, pick something? For the sake of specificity, let's say I'm interested in how British tank naming, but I'd be curious about any nation in the early 20th c.
David Fletcher is the expert on British tanks. His work British-Made Tanks of World War II provides two reasons for the naming of three different tanks. The TOG 1 and TOG 2, prototypes, were named after "The Old Gang" (Eustace Tennyson D'Eyncourt, Ernest Swinton, William Tritton, and Harry Ricardo. Fletcher implies the old gang may have comprised more, but these were the main people behind the Special Vehicle Development Committee). The A25 Harry Hopkins was named after FDR's special adviser in the UK at the time. However, Fletcher concedes "why it should [be] named after him is not known".
I am not familiar with Perter Chamberlain and Chris Ellis, but I do have a copy of their British and American Tanks of World War II. They stated the Matilda was named by the Tank Corps first commander, Hugh Elles, "due to the vehicle's diminutive size and duck-like shape and gait." The reference is lost on me though. They also state that the Valentine tank's design was submitted on St. Valentine's day and hence the name.
To answer your question "More broadly, how were these things named?", kind of randomly. Some had themes (in my other post), some were named after contemporary politicians, and some were nicknames that stuck.
A point to remember about the Mannerheim line is that the name was promoted by the Soviets for propaganda purposes, to make the line sound more formidable than it actually was after failing to breach it.
International media picked up the name and it stuck. The original name was something less exciting.