He served in the Special Operations Executive (SOE) and helped set up the Shetland Bus, an SOE operation manned by Norwegians running a clandestine route between Shetland and Norway.
For his contributions to espionage operations against the German occupation of Norway, he received King Haakon VII's Cross of Liberty.
[1] The King also made Howarth a Chevalier First Class of the Order of St Olav.
After the war, he wrote numerous books on naval and military history, including a memoir of the Shetland Bus.
He also edited My Land and My People, the first autobiography by the 14th Dalai Lama, which was published in 1962.