Veteran Squad

A number of Sternguard Veterans of the Ultramarines. And yes, the two helmetless guys might very well be Captain Titus and Sidonus in their younger years.

Though the term Veteran Squad can refer to any number of groups of experienced soldiers gathered in a single unit, in the context of Warhammer 40k this almost always means either the Hardened Veteran squads of the Imperial Guard (Read: actually survived a battle) or, more frequently, the squads consisting of the most experienced brothers of a Chapter of Space Marines.

Consisting exclusively of members of the Chapter's First Company, Veteran Squads consist of three different kinds of Battle Brothers: the Terminators, the Sternguard Veterans and the Vanguard Veterans. Though these groups maintain a sense of rivalry with one another, on the battlefield they are a lethal and efficient force.

Sternguard Veterans

The Sternguard are Tactical Marines cranked up to 11. They are the masters of the Bolter in all of its forms (In fluff, in the Crunch they have the exact same Ballistic Skill): from a standard Bolter to the Storm Bolter to various kinds of Combi-weapons all the way up to the Storm Bolter (again). They are also trained in the light support weapons used by Tactical Marines: the Flamer, the Plasma Gun, the Meltagun and the Gravgun.

Aside from the standard issue Bolt round the Sternguard Veterans are equipped with a number of different and specialized Bolter rounds:

• Dragonfire Bolts are designed to explode into a superheated gas to tell any form of cover the enemy is in to go fuck itself.
• Hellfire Bolts replace the projectile's explosive payload with mutagenic acid, designed to combat the Tyranids and all sorts of big non-vehicle targets.
• Kraken Pattern Penetrator Bolts are improved rounds with a better range and penetration.
• Vengeance Bolts are more or less miniature plasma grenades that violently explode upon impact, but are a danger to the user as well. These were designed to combat the Chaos Space Marines.

Vanguard Veterans

The Vanguard are the big brothers of the Assault Marines. Highly skilled in close-quarter fighting, they use their Jump Packs and powerful weaponry to make short work of the enemy.

Though the standard equipment of the Vanguard are the Bolt Pistol and Chainsword, they have access to the Chapter's armory to become even deadlier in combat. The most commonly used equipment for the squad consists of twin Lightning Claws and the Storm Hammer/Storm Shield combination, depending on what the mission calls for. They are also equipped with a selection of grenades.

Tyrannic War Veterans

After the Battle for Macragge, the Ultramarines formed the Tyrannic War Veterans from the survivors of the battle Companies. Trained by Ortan Cassius, their sole mission is to exterminate all Tyranids. They are more or less Sternguard with a bit of Deathwatch-light training thrown in to kill Tyranids as quickly as possible.

Tyrannic War Veterans "are" actually part of the first company, though they take their orders directly from Chaplain Cassius. They are a select group of Veterans from all companies that survived the Tyrannic Wars, but since they act as a separate unit from the rest of the chapter's organisation this meant a bit of deliberation over the Codex Astartes on the part of Marneus Calgar before they could be deployed. They all carry relics of the fallen first company, wearing armour pieced together from the previous 1st company veterans, and carrying their old bolters which they load with Hellfire shells.

They also don't recruit new members, and number only a few dozen, which will inevitably decrease over time and be replaced with "standard" 1st company veterans.

Also, with the new Tyranids Codex being the shitfest it is, the powers that be decided to drop in a Dataslate for the Tyrannic War Veterans, being a special formation whose existence is akin to kicking a dying puppy.