Press into service
Induce someone to join the military. More recently the phrase is used to mean 'make impromptu use of' some article or person to fulfil some task - usually someone or thing that isn't normally used for such a task.
British sailors really were 'pressed' into service.
In the UK in the 17th and 18th centuries hapless youths were often tricked or forced into joining the British Army or Navy by 'press gangs'. A favourite trick was to surreptitiously slip a coin into the victim's beer mug. Once they had 'accepted the King's shilling' they were deemed to have enlisted. It is rumoured the pewter tankards were fitted with glass bottoms in order to guard against this trick. Such tankards do exist but the evidence that links them to press gangs is sketchy at best. A less subtle trick was just to knock them unconscious and put them onto a ship - by the time they woke up they were on the high seas with no means of escape.
The practice was known by the early 1600s and is referred to obliquely in Robert Burton's The Anatomy of Melancholy, 1621:
"Solomon of old had a thousand concubines; Ahasuerus his eunuchs and keepers; Nero his Tigillinus panders, and bawds; they press and muster up wenches as we do soldiers"
Edward Freeman uses the figurative form of the phrase in his Historical essays, 1871:
"In Thierry's well-known History... he is pressed into the service of that writer's peculiar theories."