(set in 1927-1928, written in 1931, published in 1936)
During the winter of 1927-28 officials of the Federal government made a strange and secret investigation of certain conditions in the ancient Massachusetts seaport of Innsmouth. The public first learned of it in February, when a vast series of raids and arrests occurred, followed by the deliberate burning and dynamiting – under suitable precautions – of an enormous number of crumbling, worm-eaten, and supposedly empty houses along the abandoned waterfront … Only one paper – a tabloid always discounted because of its wild policy – mentioned the deep diving submarine that discharged torpedoes downward in the marine abyss just beyond Devil Reef.
While college student Robert Olmstead was not armed, he had a “handy three-in-one device including a screwdriver” on his key-ring. Lovecraft probably meant a flat combination tool that primarily serves as a bottle opener/cap lifter, but also has a flat screwdriver blade. These were common at the time. Alternatively he could mean a miniature pocket knife that would attach to a key-ring. Contemporary patterns usually had three blades; a bottle opener, a flat screwdriver, and a pen knife. The latter had a very short blade around 2.5-cm (1”) long that was intended for sharpening pencils and would be completely useless as a weapon.
The Federal agents would be properly armed, of course. Lovecraft does not specify from which branch of the Federal government they were. Game designer Kevin Ross suggests they were from the US Treasury Department (Escape from Innsmouth, pp. 93ff), but does not get more specific. The Secret Service would have been a good fit, having investigated the Ku Klux Klan from 1871 and dealt with foreign espionage from 1915. However, the Service did not have sufficient manpower in 1928. The hands-on Federal agency at the time was the Bureau of Prohibition, also under the Treasury Department.
For a Prohibition agent, the Colt Police Positive Special revolver (Investigator Weapons 1: The 1920s and 1930s, p. 41) in .38 Special (9×29mmR) would be typical, although many agents already liked the smaller Colt Detective Special revolver (Investigator Weapons 1, pp. 36-37) in .38 Special that had appeared in 1927. Most Federal agencies also received surplus US Army weapons, especially the Colt M1911 pistol (Investigator Weapons 1, pp. 37-38) in .45 ACP (11.43×23mm), the Colt M1917 revolver (Investigator Weapons 1, pp. 39-40) and S&W M1917 revolver in .45 ACP, and the Winchester Model 97 “Trench Gun” pump-action shotgun (Investigator Weapons 1, pp. 84-85) in 12-gauge 2.75” (18.5×70mmR). In fact, it was not unusual for agents to carry a big M1911 pistol with a Detective Special for backup. Some agents fielded privately-owned double-barrelled shotguns with sawn-off barrels (Investigator Weapons 1, p. 76).
Game designer A. Scott Glancy concurs that the Federal agents were T-Men (“Once More, From the Top” in Delta Green: Dark Theatres, p. 4). He somewhat more dramatically equips them with Auto-Ordnance Model 1921AC Thompson submachine guns (Investigator Weapons 1, p. 87-89) in .45 ACP (Delta Green: Dark Theatres, p. 18).
Lovecraft only mentions the US Navy assisting the Federal agents, but since no Federal agency had the manpower or equipment to raid all of Innsmouth, involving the US Marines in Project COVENANT is a natural choice. They had already been tasked to operate on US soil in 1926 and again in 1927, to protect the US mail.
The Marines would be armed with their standard weapons in service at the time: the Colt M1911 pistol ‒ the M1911A1 was not yet widely available ‒, the Springfield M1903 bolt-action rifle (Investigator Weapons 1, p. 72) in .30-06 (7.62×63mm), the Colt M1918 Browning automatic rifle (BAR) (Investigator Weapons 1, pp. 63-64) in .30-06, the Colt M1917 Browning machine gun (Investigator Weapons 1, pp. 94-95) in .30-06, and the AMC MK II fragmentation hand grenade (Investigator Weapons 1, p. 92). They would almost certainly also bring some Winchester Model 97 Trench pump-action shotguns and Auto-Ordnance Model 1921A and Model 1921AC submachine guns.
Glancy suggests that the latter weapons would be their primary arms (Delta Green: Dark Theatres, p. 8), but the entire Marine Corps had just 400 Thompsons in early 1928 and could not possibly hastily equip a whole battalion (over 1,050 men) in this way. However, the ratio of weapons per squad was flexible and could be adjusted depending on the task. At Innsmouth, just like in the jungles of Nicaragua, an 8-man squad would probably have two Thompson guns, one M1918 BAR, two Model 97 trench guns, and three M1903 rifles.
Note that the air-cooled, bipod-mounted Browning M1919A6 light machine gun (Delta Green: Dark Theatres, pp. 22, 32) was not introduced until 1943. The Marines would have to content themselves with the BAR and the water-cooled, tripod-mounted Browning M1917 medium machine gun, as well as the air-cooled, bipod-mounted Savage-Lewis MK VI light machine gun (Investigator Weapons 1, pp. 95-97) in .30-06. The six flamethrower teams mentioned by Glancy (Delta Green: Dark Theatres, p. 8) are likewise unlikely, as the Marines did not possess a single flamethrower during the 1920s.
According to Lovecraft, the US Navy also deployed a submarine. The most likely type to be used in 1928 was the Electric Boat Company S-class, a design built between 1918 and 1925. These boats were capable of operation in coastal areas due to their low draft. One source settles on the historical S 19 (Escape from Innsmouth, p. 142), which is quite possible. S 19 had four torpedo tubes and carried up to 12 torpedoes. The standard torpedo type at the time was the 21” (53.3 cm) Bliss-Leavitt MK 10 MOD 3 with a warhead containing 497 lbs (225 kg) of TNT ‒ not dynamite (Escape from Innsmouth, p. 146). The boat also had a 4” 50-calibre (102×885mmR) MK 9 quick-firing deck gun ‒ not a .50-calibre (12.7×99mm) Colt M1921 machine gun (Escape from Innsmouth, p. 142).