I am not a member of a
Fire Dept. but it's been
my observation that the first
apparatus on the scene is an
Engine.

The situation is quickly
evaluated,then the appropriate calls
are made,
if needed upgrades are requested.

Depending on if it is a full blown fire
call or turns out to be just a
medical emergency,unnecessary
apparatus is not tied up on a
call where it's not needed.
The first engine being virtually
a "lookout." Being first on the scene
is an extremely important responsibility.