Sledgehammer 44 is a line of comic books about the second Vril Energy Suit, Epimetheus (nicknamed Sledgehammer).
When John Severin finished his work on Witchfinder: Lost and Gone Forever, Mike Mignola asked him what he would like to work on next. Severin requested a story set in World War II, however Mignola didn't have many characters active in that era. Hellboy didn't arrive until near the close of the war and Lobster Johnson died just as it began.
There was, however, the prototype Vril Energy Suit, Prometheus, was introduced and destroyed in Lobster Johnson: The Iron Prometheus, a story set in 1937. Mignola had long planned to introduce, Epimetheus, the second V.E.S. ever since a teasing image of it appeared in B.P.R.D.: The Dead. Severin began work on the book, but unfortunately died before it could be completed. The story was shelved until a suitable artist was found.
Sledgehammer 44 was finally released as a two-issue miniseries in March 2013 with art by Jason Latour. In April, John Arcudi announced a second miniseries, three issues with art by Laurence Campbell. It was later confirmed in Hellmail along with the title, Lightning War.
A full list of Sledgehammer 44 stories can be found here: List of Sledgehammer 44 stories
Although Sledgehammer 44 has been released as a series of miniseries, in addition to numbers within a given miniseries, it also has an ongoing numbering system on the inside cover for the series overall.
The first trade will be released in May.