It is required if you are planning to travel to Ngari(Mt. Kailash, Lake Manasarovar, etc) Nyingchi (Pomi, Rawu, etc.) and some remote places in Shannan area which are regard as the military sensitive areas in Tibet. It is issued by the Military office in Lhasa. Travel agencies will arrange it as you will visit this areas. It usually takes about 3-4 days.
Ngari: all the places you will visit such as Mt. Kailash, Lake Manasorovar etc.
Nyingchi: such as Pomi, Rawu Lake etc.
Chamdo: all the places you will visit such as Chamdo, Riwoche etc.
Note: If you take a flight to Ngari from Lhasa, Urumqi or Kashgar, you will have to have Tibet Military Permit. Overlanding trip from Sichuan, Yunnan, Xinjiang or Qinghai to Tibet also require Tibet Military Permit.
Issued by the Military office in Lhasa, this permit is applied through travel agency before you entering Tibet. Due to a long procedure to get approved, you should provide your scanning copy of valid passport and visa 25 days before leaving for Tibet, if you are planning to travel any of those areas.
People with tourist (L), business (F), employment/work (Z) visa and student (X) visa have no issues to get the permit. Diplomats, journalists and government officials require arrangement by Foreign Affairs Office of Tibet Government.
The details of the travelers are required for TTB Permit: name, nationality, passport number, gender, date of birth and occupation (The copies of your passport and china visa)
Only the guide could hold the permit after you establish yourself on Tibet land. You are not allowed to bring with it.