What is "to muster troops into service"

Muster \Mus"ter\, v. t. [imp. & p. p. Mustered; p. pr. & vb. n. Mustering.] [OE. mustren, prop., to show, OF. mostrer, mustrer, moustrer, monstrer, F. montrer, fr. L. monstrare to show. See Monster.]

1. To collect and display; to assemble, as troops for parade, inspection, exercise, or the like.
   --Spenser.

2. Hence: To summon together; to enroll in service; to get together. ``Mustering all its force.''
   --Cowper.

   All the gay feathers he could muster.
   --L'Estrange.

   To muster troops into service (Mil.), to inspect and enter troops on the muster roll of the army.

   To muster troops out of service (Mil.), to register them for final payment and discharge.

   To muster up, to gather up; to succeed in obtaining; to obtain with some effort or difficulty.

   One of those who can muster up sufficient sprightliness to engage in a game of forfeits.
   --Hazlitt.