In 2012 the Wallace Collection in London staged an exhibition entitled 'The Noble Art of the Sword' with weapons drawn from many European collections, including the Royal Armouries.  I took many pictures including some of the RA's extendable rapier. 
 
I'm not sure just how practicable the design would be - unless I'm misreading the structure of the sword it doesn't actually look as if the actual length from pommel to point would change.  Only the position of the guard.  I may be wrong. 
 
Apologies for the quality of the pics - as usual it's difficult getting good shots through reflective glass.
		 
		
		
		
			
		
		
		
		
		
		
		
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