Within the 21st army group in Europe, no-one is quite sure where the idea of strapping rockets to tanks came from. Some sources suggest it was a Canadian idea, but they never followed through with it. Although there are pictures of Canadian armoured cars mounting both RP-3 rockets and Landmattress launchers.
What is certain is that the Guards Armoured Division got hold of the idea and ran with it.

The first test firing was from a Sherman tank of the Coldstream Guards 2nd Squadron, on March 17th 1945. The previous day the 2nd's commander had undertaken a social call to the local RAF airbase and came away with a set of RP-3 rockets and launching rails.
After spending the next morning welding the rails to his tank, they stood a safe distance away and connected the battery.
The rocket leapt off the rails, and dropped down to almost hit the ground in front of the tank, then recovered and zoomed off blasting a crater in a hill a good distance away. The drop of the rocket was caused by the difference in launching speeds. Normally when fired from an aircraft the rocket is doing 400 mph, while the Sherman is effectively doing 0 mph. This was solved by aiming the Launching rails slightly upwards.

The next few days were spent finding enough launching rails and rockets, and converting the tanks of the squadron.Almost daily there were demonstrations to visiting brass who had heard of the novel idea. Culminating on the 28th with a demonstration for the Guards Armoured Division commander, where an entire troop launched a full broadside. The division commander was so impressed he is reported to be rolling on the floor laughing at the idea of lobbing the equivalent of a cruisers broadside at the Germans.

Tanks fitted with the rocket rails were named "Tulips". As the project was unofficial and carried out by the battalion fitters its not entirely clear how many tanks were converted. Its almost certain that the entirety of the Coldstream guards were converted. There are some pictures of Cromwell tanks carrying Tulip's, and the Welsh Guards had those. The markings on the Cromwell tanks so photographed don't carry the divisional symbol, but what markings do exist do follow a patten used by the Welsh Guards. So its conceivable the other regiments within the Guards Armoured Division converted some tanks. Both Sherman's and Fireflies were converted to carry Tulip kits.

Tulips were first used in anger on Easter Sunday (April 1st) 1945. The 2nd squadron, Coldstream Guards were trying to find a bridge over the Twente Canal. They had reports that a bridge at Enschede was still standing. As they drove along the road beside the canal a frantic Dutch man ran up to the column of armorued vehicles. Unable to understand him they had to push on as their orders required.

(Note: The following all happened in a very short space of time, and is compiled from the eye witness accounts of most of the tank commanders involved. Remember they will only have seen their small part of the action. I've tried to lay it out in order, but it should be remembered that sometimes mere seconds separated the items bellow.)
Suddenly the tanks saw the bridge less than a quarter of a mile away, and it was swarming with Germans! As the tanks rushed forward they scattered the Germans on the bridge with machine gun fire.
The lead two Sherman tanks, two Daimler Armoured Cars and a Daimler Dingo rushed over the Bridge. As they drove over they saw 4 huge demolition charges on the bridge. The armoured cars halted on the other side of the bridge and the crews dismounted to try and disarm the demolitions.
On the other side of the bridge the next tank in line, a Firefly had spotted four German 105mm Artillery pieces dug in 150 yards away on the other side of the canal, and covering the road. Stopping the Firefly started to engage them, then after a few round roared off over the bridge.
The next tank in line halted behind the stationary Firefly hit one of the German guns with a 75mm Shell, then as his Browning was still empty, launched his Tulips, destroying one of the other guns. The Germans then fired hitting the halted Sherman just behind the turret. If the round had gone as little as 6 inches higher it would have missed completely. The Sherman burst into flames, the fireball engulfed the tank behind it as well.
At this point the Germans detonated the charges on the bridge, dropping the span.
The next Sherman in line was making as much smoke as possible while reversing. An AP shell smashed a tree to bits right next to the tank as the Sherman reversed through a barn. The next round knocked out the Sherman's tracks. At this point the column had disengaged successfully, later in the day they would return and capture the village.

On the German side of the bridge the Firefly which had gotten across was hit in the turret and knocked out and the armoured car's crews were killed by the bridge being detonated. The second Sherman across managed to avoid the Germans and followed the canal, managing to cross much further down and re-joined the regiment.
The first Sherman across had started pushing into German held lines, getting half a mile further on when they heard the bridge blow up. So they returned to see what had happened. The tank wash it by three Panzerfaust's and survived with no damage, then an AT gun round struck it, knocking its track off. The tank was moving when this happened and rolled down an embankment, and out of the line of fire for the gun. The crew bailed out and managed to rejoin the regiment by stripping naked and swimming across the canal.

The reason for the German gun's poor showing was that earlier in the day the 105mm's had a visit from Typhoons of the RAF, and the gun crews had all fled, leaving infantry to try and man the guns.
Not the best of starts to the career of the Tulips, although it should be noted that 12 of the POW's whom had been captured later in the day were deaf from being too close to the Tulip shots.

Despite this lack of impact in its first action the Coldstream Guards continued to use Tulips until the end of the war. They proved their worth many times over, with one tank commander crediting the presence of Tulips as being the reason they took far less casualties than expected. One engagement demonstrates this perfectly.
German paratroopers from the 7th Fallschirmjager Division had turned a wood into a strong point, and was severely delaying the advance and causing heavy casualties to the allied infantry. Two troops of Tulips arrived and fired their rockets at the range of 400 yards. The Germans instantly surrendered, and were described in a report as "very shaken".
It was also found that Tulips were very good at removing roadblocks where AP and HE rounds had failed.

A post war report into mounting rockets on tanks stresses how safe the rockets are. Pointing to the fact that one rocket was hit directly in the warhead to no effect apart from shattering the round. Another account points out that despite a Sherman being set on fire, it was later found that both rockets were still in place.
The report also starts to talk about uses against AFV's, and how if the accuracy could be improved rockets would make a fine Anti-tank weapon. The report is largely supportive of the idea of future development of rockets as part of armour.
Then the report reaches the Ministry of Supply where the Director General writes off the idea as a silly one due to the lack of accuracy.