Double check

A quick look at the forcing nature of double checks

A double check, as the name suggests, is a check delivered by two pieces at the same time. While not technically a tactic (as it is not a sequence of moves), a double check can play important roles in a sequence due its very forcing nature: the only legal moves are king moves.

A beautiful application of double checks often occurs in smothered mates:

1. Nh6+ is a double check (as both the knight and the queen deliver check simultaneously). and it is the start of a beautiful sequence because Kh8 is the only possible response.