Sunday Express

[Lottieman]

27 across, A Japanese martial art characterised by stealthy movement and camouflage that is practised by ninja. (8 letters) -i-j-t-u

Ninjitsu or Ninjutsu, both would fit

[baitress]

My Dictionary shows ninjutsu

[Stockethill]

My one says jiujitsu.

[Lottieman]

Thanks Baitress, Chambers give both, I'll go with your suggestion