It should be noted that the military and athletics are both areas that tend to select for people with good sleep to start with (since poor sleep has negative impact on the things they look for) and then often overwork people. So the high success rate is not surprising in those conditions. Sleep is not just the result of both physical and mental relaxation, although most people are likely to be able to sleep in that situation. Every self help book on sleep has varitions of this technique and many people find it helpful, but not everyone is able to sleep quickly even with relaxation.