As the Previous posters have very correctly stated,you will be trained in the vehicles that you use as part of the job.
You will not be " given " the licences,but will be trained and if not up to standard possibly not pass....being able to drive is a skill beyond some people.
For Example a Royal Engineer Driver Specialist would pretty much go like this
Combat Engineer/Driver B3
Initial Training in car licence and LGV 3 after Combat Engineer training....when you get to unit you will be taught to drive the specific vehicles associated with that licence...4 ton Bedford...landrover,trailers and most likely pick up an ADR licence as Sappers like to carry things that go boom.
Possibly pick up your tracked licence for Spartan of AFV432 if your a section driver
Driver B2
In house training..after proving your capable of not killing your passengers you move up to the next pay scale and drive the 14 tonners for example, and Drops getting your LGV2 at this point.
Bus licence trained in unit if you bribe them with beer.
Driver B1
This is where you get the chance to learn and drive the Engineer toys like self loading dump trucks and Foden Tippers,Ivecos ( if they still use them ) recovery trailers,full size tankers ( beer bribe ),Boat trailers.
Driver Specialist
1) Royal Engineer Crane Operator ( CPCS crane )
2) Plant Transporter ( HGV 1 )
3 ) Tank Bridge Transporter ( Freaking huge )
4 ) Able Bridging System
I also managed to pick up my Road Roller licence,Tracked Licence on a D6 dozer and motorcycle licence plus a full bus licence during this time.
** on a super serious note....if you cannot understand why someone needs a Bike licence...nobody will be able to explain it to you.My bike licence was the hardest test out of every licence I took and is the one that I have used the most in relation to travel,fun and pure pleasure.