After certain incidents within the Royal Navy (http://en.wikipedia.org/wiki/2007_Iranian_seizure_of_Royal_N...) the training programme has changed to deliver more "Grit and Determination".

To answer the question on how to train it, the RN believes that it's done by pushing people through difficult situations during training and showing what's possible. I'm not convinced it's possible to self-improve grit to any significant level.