There are, I have always believed, two types of valour: spur-of-the-moment bravery and what I call cold courage, which involves planning.
I've nothing but admiration for those decorated for impulsive bravery: a serviceman who, in the heat of battle, risks his life to save a wounded comrade.
Many such men have rightly been awarded the Victoria Cross, Britain's top military bravery medal.
But my new book, Special Forces Heroes, deals with those awarded medals for acts of premeditated courage.
It takes a special kind of valour to go undercover behind enemy lines or to be part of a small, elite unit on a hit-and-run mission against a far larger force.
If it goes wrong, he knows that, at best, he might be captured and kept as a prisoner of war for months, even years.
At worst, he might be seized, tortured, mutilated and killed.
Not everyone mentioned in my book was a member of the Special Forces, but one account chosen here relates to the SAS.
The first - the Battle of Mirbat in Oman in 1972, which saw a handful of SAS men fight off 250 heavily armed, rebel fighters - is not well-known, but is considered by a growing number of military historians to be the regiment's finest hour.
The second involves what must surely be the most celebrated moment in the regiment's history - the storming of the Iranian Embassy in 1980.
Battle of Mirbat
(JULY 19, 1972)
Trooper Sekonaia Takavesi
Distinguished Conduct Medal
Oman, a long-standing ally of Britain, is a forgotten war - not least because the SAS's involvement in protecting the country's sultan from the Communist rebels of the People's Front for the Liberation of the Occupied Arab Gulf (PFLOAG) was top secret.
Not even the families of those fighting knew where they were.
But by July 1972, the regiment had been training and advising local troops in the small Gulf state for a year.
Operation Jaguar, designed to consolidate their positions, establish new ones and disrupt rebels lines of communications and resupply was going well.
Then, at dawn on the morning of July 19, the rebels hit back, with 250 of their elite fighters attacking the small town of Mirbat on the Arabian Sea.
They were heavily armed and their aim was to overrun the town and slaughter everyone in their path.
In the town's garrison were just nine SAS soldiers, equipped with one 25-pounder field gun from World War II, one mortar, a 0.50mm machine gun and a few general purpose machine guns.
When the adoo (Arabic for enemy forces) attacked, all the SAS men were in the British Army Training Team (BATT) house, 500 yards from the gun pit containing the 25-pounder.
But when they heard mortar rounds and machine gun fire from an outlying observation point, they moved swiftly.
A Fijian trooper called Talaiasi Labalaba ran to the gun pit and, though it normally took a three-man team to operate it, managed to open fire by himself, sighting the gun down the barrel and firing into the advancing rebels at near point-blank range.
Mirbat castle: Scene of a ferocious battle in Oman which is considered to be the regiment's finest hour
But when Labalaba was wounded, hit in the chin by a 7.62 mm round from a Kalashnikov rifle, it seemed only a matter of time before first the gun and then the garrison were over-run.
But for the decisive action of his fellow Fijian, Sekonaia Takavesi, it probably would have been.
Known as 'Sek' or 'Tak' to his friends, he became - in the words of his Army superiors - 'a legend in his own time within the SAS'. Grabbing his rifle and a few magazines, he sprinted to the gun pit and found his friend badly injured, his jaw smashed, but still continuing to fire the gun. Realising they needed more support, Takavesi left the gun pit, running to a nearby building to persuade an Omani gunner, Walid Khamis, to join them. Now there were three: Labalaba and Khamis operating the 25-pounder, while Takavesi used a self-loading rifle (SLR). But as enemy fire pounded the gun pit, Khamis slumped backwards. He had been shot in the stomach and was writhing in agony. The two Fijians were on their own again, with Takavesi helping his friend, time and again, to remove the hot shell case, ram in a new one, close the breech and fire.
Soon it was Takavesi's turn to take a bullet, which threw him backwards on to the sandbags. He was in great pain and losing a lot of blood, but he remained conscious.
Labalaba propped him up and handed him his SLR. Labalaba, who was peering down his rifle sights picking off the advancing enemy, realised he was almost out of ammunition for the 25-pounder.
As he tried to reach a 60mm mortar positioned nearby, he was shot fatally in the neck.
In the BATT house, Captain Mike Kealy heard the 25-pounder fall silent and became worried the position had been taken. With a volunteer, Tommy Tobin, a trained medic, the commanding officer dodged bullets and ran to the gun pit, where they witnessed a gruesome scene. The dead body of Labalaba lay face down on the ground, Khamis was lying on his back, bleeding profusely.
The only one still able to fire was Takavesi, who, still propped on the sandbags, was also seriously wounded. Every time he fired his SLR, he grimaced with pain as the rifle kicked back into his body.
As Tobin turned to get his medical pack, he was shot in the face and fell to the floor mortally wounded.
Pete Scholey, a former SAS man and author of SAS Heroes: Remarkable Soldiers provides an account of what happened next. 'Tak called to Captain Kealy for more ammunition and the two men began to battle for their lives. An adoo popped up at the edge of the gun emplacement, ready to shoot Tak, and Kealy blasted him with his SLR.
'Another appeared from a ditch close to their position and Kealy cut him down, too. Kealy took out adoo gunmen as they slunk round the walls of the fort and Tak concentrated on those coming from the direction of the perimeter wire. The adoo were close enough to sling grenades, which were bouncing and exploding close to the walls of the gun pit. Kealy froze for an instant as a grenade landed inside the bunker right in front of him. Mercifully, it failed to explode.'
Just as the situation appeared hopeless, the two men and their comrades had two strokes of luck.
First, the low cloud lifted high enough for two jets from the Sultan of Oman's air force to fly over the scene, strafing the adoo with cannon fire and, at one point, dropping a 500lb bomb on the by now retreating rebels.
Takavesi, who was later involved in the storming of the Iranian Embassy, would later describe the scream of those jets as 'the best sound I ever heard'.
Kealy was unaware of the second stroke of luck, which resulted from his early radio message to SAS headquarters that Mirbat was under attack. His men, B Squadron, had been due to go home on the very day of the attack.
This meant their replacements from G Squadron were at Um al Quarif, just 65km west of Mirbat. G Squadron was ordered into action.
Twenty-two men, along with their equipment, were taken by trucks to the airstrip at Salalah. Once the mist had lifted, they were airlifted in helicopters to the beach on the edge of Mirbat.
As Kealy used a lull in the fighting to tend to his men, G Squadron, led by Captain Alastair Morrison - another SAS hero who would go on to play a vital role in the successful storming of a hijacked Lufthansa jet at Mogadishu airport in 1977 - fought its way through the town.
The adoo were in full retreat, leaving 40 dead and ten wounded.
It had been an incredibly close run thing, but thanks to the bravery of men such as Takavesi, Labalaba and Kealy, it proved to be a decisive turning point in the sultan's battle with the rebels.
The Battle of Mirbat is an extraordinary story and I share the sense of anger among SAS men that the bravery of the solders involved has never been properly recognised.
As a result, I have sponsored the Battle of Mirbat Memorial at the National Memorial Arboretum in Staffordshire.
The valour of men such as Takavesi, Labalaba (who many believe deserves a posthumous Victoria Cross) and Kealy - three of the great Special Forces heroes - should never be forgotten