Most of the characters in Orphanage are orphans of one form or another. Kinetic weapons from what appears to be an alien colony on Ganymede are devastating the world, killing millions. A multinational force is being put together in order to take the war to the enemies door - and Jason Wander is part of it. Driven to despair by the death of his mother in one of the first attacks, he signs up in the military to avoid a prison sentence. It's an unnatrractive alternative that finally helps him realise who he is, to find love and friendship, and a purpose. In the orphanage of war he finds a new family. Jason's story mixes military service with a touch of detective work into the true nature of the foe (alongside a forgiveable authorial trait of using authorial fiat to put him in the right place at the right time).
This is the positive side of military SF, a novel like Haldeman's Forever War that takes war and uses it to explore its effects on the people involved. This isn't a story of glory and of overwhelming might. It's the tale of a suicide mission with little hope of return, and of the people who choose it over the alternatives. Jason Wander is a flawed character who surmounts his flaws to take advantage of lucky accidents and to find an impossible route to some kind of victory.
An enjoyable read, avoiding much of mil-SF's didactic nature.