You need to find the actuating mechanism for the WW1 Marlin gun and increase the rate of fire. I have seen hats like the officer's for sale in various surplus sites.
Fleet tug? The USN was about to find out that their 6mm guns were outranged.
I read somewhere that the Rough Rider's Colt-Browning guns were purchased by the Tiffany family of NYC. Not the fancy lamp guy, but his brother, from the same wealthy family. William Tiffany was a Sgt and actually commanded the machine gun crews.
Lt. Parker, a regular, not a Rough Rider, commanded the Army's Gatling gun unit, & coordinated efforts with Sgt Tiffany. Tiffany introduced Parker to TR. After TR became Pres, Parker became a frequent White House visitor, got to be a bird Col and was put in charge of making the Army's machine gun program worked.