An Immediate Assault is initiated against an enemy in a chance contact, or in a hard contact not severe enough to suppress your team. It is used defensively in order to quickly make and then break undesirable but unavoidable contact, or offensively to quickly gain the upper hand against an enemy and to decisively engage them.
When there is essentially a hard contact for both sides; Either force only knows about each other at approximately the same time, relatively close to each other and without warning. The significance of this is that neither force is prepared for the engagement, so which force gains the advantage (besides size, preparedness and equipment) depends on which force reacts the most decisively, the quickest and with the most aggression. A good example of a Chance Contact drill is an Immediate Assault. – DTT Contact
When any member of a team happens upon a chance or hard contact, then that member may automatically commence an Immediate Assault by firing at the enemy and calling out their direction. Then the rest of the team moves into line with, and engages the enemy.
An immediate assault is executed properly when all the firepower of the team is brought to bear against the contact within a few seconds of the first shots, all in the correct direction and with the team in the optimal position and formation (usually a line) to engage the enemy and then to either commence Fire & Movement, or a Peel, depending on the assessment of the team leader.
The drill ends when the team has transitioned into another drill such as a Fire & Movement or Peel, or if the enemy has been destroyed or withdrawn and destruction of the enemy is not necessary.