Most of the information here is for Warzone 3.1 and above.
c002 transcript
Sequence
Briefing commences.
Team Beta is searching this sector for Vertical Take-Off and Landing, VTOL, technology.
This is believed to be located at a pre-collapse air base in this sector.
Team Beta is currently under attack from an enemy force know as "The Collective". Analysis indicates that The Collective are more technologically advanced than us. Be prepared for aerial as well as ground attacks.
(Male voice:) Team 3 reporting.
(Male voice:) All quiet in sector 12.
(Male voice:) Heading back to base.
Upon arrival you are to assume command of the base. You must defend it and hold it.
Be sure to fortify the perimeter and establish anti-aircraft defences.
New technologies are available.
Duplicates
Several other sequences include sections of the c002 sequence, which is somewhat unusual...
It would appear that Pumpkin Studios tried a few different approaches to the start of Beta Campaign: The Collective and the sequences from those approaches survived.
The cam2int1 sequence contains additional footage of the Beta base under attack.