Virtually all nations in World War One had a periscope trench rifle of some sort, and the United States was no exception – although it was not formally adopted. The Cameron-Yaggi conversion was developed by James Cameron and Lawrence Yaggi of Cleveland Ohio, and submitted to the US Ordnance Department in late 1917. About 12 prototypes were made in total, all slightly different – and none was actually adopted before the war ended.
The Cameron-Yaggi conversion is notable for its rigidity and smooth operation, allowing sighting, firing, and bolt cycling from a concealed position. Most trench rifles are rather rickety devices, but not this one. Both 1x and 4x magnified periscope sights were experimented with, and a 25-round extended magazine was fitted in order to maximize the utility of being able to operate the bolt from the firing position. The device added about 6 pounds to the weight of the rifle, which certainly helped reduce recoil – and it did not require and significant modification to the host rifle!
This Cameron-Yaggi conversion is from the Bruce Canfield collection, previously in the Brophy collection.