Cave diving uses that phrase as well. I suspect it does originate in the military, though, and probably reloading guns and cannons while under fire. Might go

Cave diving uses that phrase as well. I suspect it does originate in the military, though, and probably reloading guns and cannons while under fire. Might go back further than that to bows and arrows. Looks like a related term "make haste slowly" dates back to Roman times and was applied to military commanders: https://en.wikipedia.org/wiki/Festina_lente https://en.wikipedia.org/wiki/Festina_lente