Building your Army - Detachments and Formations

This is a quick reference to help with questions about Detachments and Formations. For full details please read your rulebook – pages 116 – 122.


Units are the basic building block of every army. In current style Codexes, each unit has a full-page ‘dataslate’ entry. In older Codexes they have an army list entry.

Example Units

  • Space Marine Tactical Squad. See Codex: Space Marines
  • Eldar Farseer. See Codex: Craftworlds
  • Astra Militarum Leman Russ Squadron. See Codex: Astra Militarum


Formations are one way of choosing a grouping of units. Each Formation has a full-page ‘dataslate’ entry. It lists which specific Units make up the Formation, and may have some restrictions on how they can be equipped. Formations give additional special rules to some or all of the units in them.

When a Unit is chosen as part of a Formation, that unit may not belong to any other Formation or Detachment in the army.

Example Formations

  • Space Marine Battle Demi-Company. See Codex: Space Marines
  • Eldar Aspect Host. See Codex: Craftworlds
  • Dark Eldar Corpsethief Claw. See Codex Supplement: Haemonculus Covens

Unbound Army

One of the methods of choosing an army is Unbound. To choose an Unbound army, you take any combination of Units and Formations that adds up to your agreed points level (or below).

Unbound armies may not use Detachments.

Note: although Unbound is a legal army building method according to the rulebook, it is not commonly used by players. You should expect to have a conversation with your opponent about why you’re playing Unbound and whether they’re ok with it.


Detachments are the other way of choosing a grouping of units. A Detachment has a number of choices or slots for units with different Battlefield Roles, with minimum and maximum numbers allowed for each. It may have additional restrictions. Detachments give additional special rules to some or all of the units in them.

When a Unit is chosen as part of a Detachment, that unit may not belong to any other Formation or Detachment in the army.

Example Detachments

  • Combined Arms Detachment (often called “CAD”). See Rulebook
  • Ministorum Delegation. See Codex: Imperial Agents
  • Castellans of the Imperium. See The Gathering Storm Part 1: Fall of Cadia

Decurion-style Detachments

Called Decurion-style after the first one to be published – the Necron Decurion. These are a special kind of Detachment. Instead of having slots for Units, they have slots for choosing Formations. Each one will list the specific Formations that can be taken.

Decurion-style Detachments are an exception to the normal rules, in that units in it belong to both the Formation they are chosen in, and the Decurion-style Detachment. They may gain special rules from both.

Example Decurion-style Detachments

  • Decurion. See Codex: Necrons
  • Gladius Strike Force. See Codex: Space Marines

Battle-Forged Army

This is the common way in which players choose armies. To choose a Battle-Forged army, you take any combination of Formations and Detachments that adds up to your agreed points level (or below). This might include Decurion-style detachments.

Tournament Restrictions

In the standard 40k rules there is no restriction on the number of Formations or Detachments taken, as long as each is valid. (Since 7th Edition – older editions were more restrictive). However, most tournament formats do restrict the number. For example, in the ITC format you may not take more than 3 Detachments or Formations in total.


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