Re: What's that engine?

In detail view the loco is clearly a Mogul. It was probably a US military engine organic to this unit--the 41st Coastal Artillery was a rail-transported anti-ship artillery unit.
41st FIELD ARTILLERY
Constituted 26 August 1918 in the Regular Army as the 41st Artillery (Coast Artillery Corps)
Organized 1 October 1918 at Fort Monroe, Virginia
Demobilized 22 December 1918 at Fort Monroe, Virginia
Reconstituted 15 January 1921 in the Regular Army as the Hawaiian Railway Battalion
Organized 22 December 1921 at Fort Kamehameha, Hawaii
Redesignated 1 June 1922 as the 41st Artillery Battalion (Railway) (Coast Artillery Corps)
Reorganized and redesignated 1 July 1924 as the 41st Coast Artillery
Inactivated (less 1st Battalion) 30 June 1931 at Fort Kamehameha, Hawaii
Activated (less 1st Battalion) 21 April 1942 at Fort Hase, Hawaii
Disbanded (less Batteries A, D, and G) 25 May 1944 at Fort Kamehameha, Hawaii (Batteries D and G - hereafter separate lineages) (Battery A concurrently reorganized and redesignated as the 831st Coast Artillery Battery; disbanded 13 August 1944 at Fort Kamehameha, Hawaii)