The description of one Alco S2 will suffice for all of them. 

It was a 1000 hp switcher with Alco's Blunt trucks,  powered by Alco’s 539 turbocharged, 6 cylinder diesels,

Number 20, along with her sister number 21 were part of order S-1892 from Alco. The two S-2s cost $53,000.

Each supplied a tractive effort of 57,000 lbs, just slightly more than twice what the most powerful and efficient of the steamers could do.