What is the most efficient technique used to gain altitude with a fighter? Or any other plane for that matter. I have seen many ways of doing it.

 - The simplest being a standard climb by accelerating forward at a
   slightly upward angle.
   
 - But I have also used a series of [Immelmann's][1] to acheive the
   desired height.

Is there any other techniques that use a different game mechanic to acheive a certain altitude the fastest?

[1]:http://wiki.warthunder.com/index.php?title=Combat#Immelmann "War Thunder Encyclopedia"