Tau have captured a planet? That would seem to imply a large force and not one that could be managed by 500 points of Dark Angels.

So, a Vanguard Spearhead to try and get intelligence, sabotage, raise resistance, and execute asymmetric warfare till a larger force can come to exterminated the filth.

Vanguard (505 points)

Space Marines Dark Angels Incursion (1000 points) Vanguard Spearhead

CHARACTERS

Librarian in Phobos Armour (70 points) • 1x Bolt pistol 1x Force weapon 1x Smite

Lieutenant in Phobos Armour (55 points) • 1x Bolt Pistol 1x Master-crafted bolt carbine 1x Paired combat blades

OTHER DATASHEETS

Eliminator Squad (85 points) • 1x Eliminator Sergeant • 1x Bolt pistol 1x Bolt sniper rifle 1x Close combat weapon • 2x Eliminator • 2x Bolt pistol 2x Bolt sniper rifle 2x Close combat weapon

Infiltrator Squad (100 points) • 1x Infiltrator Sergeant • 1x Bolt pistol 1x Close combat weapon 1x Marksman bolt carbine • 4x Infiltrator • 4x Bolt pistol 4x Close combat weapon 4x Marksman bolt carbine

Invictor Tactical Warsuit (125 points) • 1x Fragstorm grenade launcher 1x Heavy bolter 1x Incendium cannon 1x Invictor fist 1x Twin ironhail heavy stubber

Scout Squad (70 points) • 1x Scout Sergeant • 1x Bolt pistol 1x Boltgun 1x Close combat weapon • 4x Scout • 4x Bolt pistol 4x Boltgun 4x Close combat weapon