Doc AV seems to have made a mistake on this one, a truly unique event, compared to his usually complete and accurate info which is most informative. The “1 pounder” is 37mm (1.5" +/-) diameter.
The projectile is U.S. Navy 1-pounder Mark V solid steel projectile, either an armor piercing “shot” which would probably be hardened, or unhardened as a “common” (non-explosive) projectile, used for most purposes. I was not able to find exact reference to the Mark V projectile to see if it was intended for use exclusively with the 37 x 93mm “1 pounder” or the longer cased “Heavy 1 pounder” or perhaps both. Various “Marks” were assigned to distinguish between projectile types, typically some being AP, high explosive, common, or practice.
As Doc AV correctly noted, it was made by Toledo Screw Products Co., and the 17 preceding the maker name is the date of manufacture. Lot 197 is a production lot number assigned for tracking and quality control purposes. The anchor/RRA and anchor/JA in oval are inspector and acceptance markings.
These 37mm guns were used in a variety of single shot, rotary Hotchkiss, or recoil operated Maxim machine gun type guns circa 1885-1920s. The various types of guns are well described at http://www.navweaps.com/Weapons/WNUS_1pounder_m1.php#Ammunition
The 37mm guns continued in use as sub-caliber guns attached to a ship’s larger guns for economical target practice with much smaller danger spaces beyond the target.
Being made of solid steel with a copper rotating band (driving band to Army guys) it is totally safe and inert.