Mandalorian Federation Remnant

The Mandalorian Federation Remnant was a brief splinter group that rallied behind Raylen Eros to attack the Sith supercruiser Prometheus during the Battle of Polis Massa.

Battle of Polis Massa
See the above link

Numbers
The Federation Remnant had three Federation cruisers and consisted of roughly 150 personnel on board the Polis Massa station.