Lt. Col. John Malcolm Fleming Thorpe Churchill is a man surrounded by misinformation, rumors, and exaggeration. This really bothers me, so I'm gonna try to list some of the misconceptions I've heard and give proof of them being wrong.
This is obviously the most common rumor you hear, and is in fact not wrong, it it correct. *However*, it is an exaggeration through ambiguity. You must understand that "claymore" is not a specific sword, it is in fact two different swords that go by the same name. The most well known claymore is a greatsword, usually at least as tall as its weilder, and usually bearing a V-shaped crossguard. The other claymore is a sidesword, bearing a one handed basket hilt, with a blade not longer than two feet usually. The basket hilted claymore can also be called a claybeg or a backsword. This is the sort of claymore Mad Jack carried. Look at this image:
If you look to the right of the photo, you can see a soldier carrying in his right hand an object that looks like a white wedge. That object is a basket hilted claymore, that soldier is Jack Churchill, and that photo was taken in 1940, when the Fighting Jack led a training exercise with his No. 2 Commando in Inveraray, which is a town in Scotland.
This is perhaps the second most common rumor, and it goes something like this: Mad Jack was fighting on the isle of Brach, and led his commando in a charge up a hill to assault a German fortification there, he pressed on to the top of the hill without realizing that by the time he reached the top he was the last man alive. In a fit of his usual insanity, he decided to play the bagpipes because why not, at which point a few Germans started throwing grenades at him until he was knocked out. This story is wrong for many reasons, first, Mad Jack was actually not as insane as common belief would have it. He was placed in charge of an entire commando brigade, and the British Army was not known to put insane people in important positions, so it would be very difficult for him to be as insane as common myth would have it. Second, no way is it possible that he just "didn't notice" that all his men were dead. He's an officer, he is meant to be protecting and looking out for his men. Someone who is so absentminded or inattentive that they can suffer 100% losses before noticing it would not be put in charge of an entire brigade. Third, grenades don't just knock you out, they kill you. This one is a no brainer, needs no explanation. If Germans were able to throw grenades directly at him, they would've killed him, but they didn't.
Now, let me explain things as they happened, according to the man himself. Unsurprisingly the real story holds all the elements which would inspire the exaggeration. Churchill was in charge of an operation to capture several hills on the isle of Brach, in an operation involving No. 43 Commando and No. 40 Royal Marines Commando. When Jack arrived at the starting point of the attack well after he thought that they should've started, he found 40 Commando standing around doing nothing, and 43 Commando to be absent. He asked 40 why they were down here and not ontop of the hill, and they told him that they were held up by barbed wire and mines. Jack said, "Barbed wire and mines? How many men have been killed?", and was told that no one had been killed and no one wounded. Through a few more questions, Jack discovered that the men had not dug up a mine, and had no actual proof of a minefield being there, other than two posts that looked suspiciously like how Germans mark minefields. Jack told them that they were being stupid, because the only way to mine a hill like the one they thought was mined was with tripwires, so he told them to walk up the hill and take big steps up, so they could step over any tripwires. They did this, and no man was killed or injured.
Later it was discovered that the reason 43 Commando was absent was because the messenger who was supposed to have informed them about the plan of attack several hours ago had gotten lost,and as such 43 Commando was eating their dinner in blissful ignorance. Jack still thought that 43 should be somewhere nearby, so when he got to the top of the hill with 40, he sent the commander of 40RM, Lt. Col. James Calvert Manners, to the left, and Capt. Edward Roger Wakefield to the right, to hopefully spot 43. Manners went roughly 20 yards, before he fell down and yelled, "I've been hit!" and Churchill shouted to him "Alright, I'm coming to get you!". So Churchill made his way over to Manners, and then dragged him to a safer position out of the line of German fire. As Jack started patching up Manners, who had been hit in the upper part of his chest near his shoulder, Wakefield came over to them and said, "I've been hit too." So now Churchill was lying down in the grass on a hill, trying to keep his head down from German fire, with a wounded Lt. Col. and Capt. on his hands. As he was working on binding up the wounds of his two officers, a Marine came over, and Jack told him to help. The Marine started to do this, but didn't get very far before he was hit in the head and collapsed ontop of Wakefield, dead. Jack pulled the dead man off Wakefield, and finished patching up both officers. He then rolled onto his back, pulled out his bagpipes, and played "Will Ye No Come Back Again". The song is significant here, as he was using this as a signal to 43 and 40RM Commandos, hoping they would hear him playing and assume he was in trouble, or at least they would recognize the song and think that maybe they should come back(because that's the name of the song). Unfortunately for Jack, no one came to his aid, and he was eventually hit in the head by a splinter from a mortar, which would have killed him if not for his steel helmet, which I believe to be a MK I*, based on his description and the few pictures we have. Jack was knocked out, and the hill was taken again by the Germans by the time he woke up. Both Manners and Wakefield died that night from their wounds.
My source: an Imperial War Museum recording of an interview with Mad Jack himself, March 5th, 1986