Whole plasma may be stored frozen, or it may be stored dry. Dried plasma can be flown anywhere in the world, and is vital for the armed forces. The method was invented in the USA in 1940, and used widely in World War II. The Army/Navy standard pack was two tin cans, each with 400cc bottles inside. One held the plasma, the other distilled (pure) water. The plasma could be restored in three minutes, and remained fresh for about four hours.