Reconnaissance Squad

Back when Scouts kicked plenty of asses.

The eyes and ears of the Legions, the Reconnaissance Squads are the spiritual predecessors of the modern-day Scouts.

Back in the times of the Great Crusade, the Legion's recruitment differed from what current day Chapters do. Once a recruit passed their training, they got their armor and gear (just like Grey Knights and Space Wolves practice), thus there were no Scouts. Recon Squads are roided-up Scouts with power armour (Originally the Mark II: Crusade Armour, but later upgraded to the Mark IV: Maximus Armour), sniper rifles, nemesis bolters, cameleoline and a set of gear like the Nuncio Vox (though they can take other weapons like bolters, shotguns and melee weapons). Military experts trained in the art of sabotage, raiding, intel-gathering, assassination, stealth and recon deep behind enemy lines, these guys usually don't go head-on in a fight. Yet when there is no room for stealth and there was a open battle, these individuals quickly switched to flanking maneuvers and infiltration attacks while supporting their main forces.

After the Horus Heresy and the splitting of the Legions into smaller Chapters during the 2nd Founding, the modern-day Scouts emerged replacing the Reconnaissance Squads completely. In the 42nd Millennium after the introduction of the Primaris Marines, this unit actually got an actual spiritual successor in the form of Infiltrator and Eliminator Squads of the Vanguard Primaris.

Crunch

Crunchwise, they are Space Marines that like stealth and are tactical. The cheapest scoring unit, as they have the Line sub-type and cost 85 points, with the standard Vexilla, Nuncio-Vox and Augury scanner upgrades optional. However, they are Support Squads and cannot be taken as Compulsory choices. Though 85 points only nets you five men, they come with a lot of goodies. First, they have the Scout and Infiltrate rules, so they are flexible with deployment options. They also have Shroud Bombs, and so count as being 6" further for the purposes of trying to shoot at them, and Melta Bombs are also an option. They come with Bolters and can be equipped with bayonets or they can be swapped out for shotguns, which became a little bit different with the addition of the Concussive (1) rule. They can also swap them for chainswords if you want extra Shred attacks, but what is probably the most effective use of them is to fork out points to give them Nemesis Bolters and make them a squad of Character assassins. You are allowed to mix and match weapons if you want and while this might not be the most efficient choice, it can allow for double debuffs of Concussive (1) and Pinning in a single volley of shooting.