Probably. As always, Kancolle devs are always vague with this kind of stuff.
At first glance, it looked like only the US Navy used the imperial system, but as it turned out, the British had also used imperial systems during WW2 as well, and they didn't really adopt the metric system until 1965, which is about 20 years after the war.
So yeah, these guns are indeed are from British origin which can be traced to the Nelson-class battleships. It also can be noted that the Nelson-class are two of the Big 7 battleships that have the 16-inch caliber main guns, and had Imperial Japan not petition for Mutsu to be spared from the scrapyard, the Big 7 would've been the Big 2 instead, with only Nagato and one of the Colorado-class battleship, which somewhat explains why their fairies looked somewhat like blonde Mutsu.