I was taught that the Thin Red Line was an important part of the transition from smooth-bore muskets to rifles, as rifles were far more accurate than muskets, could shoot greater distances, and were more lethal. and allowed Campbell's men to stop the cavalry charge sooner. I'm told this paved the way for making the square formation obsolete, and cavalry charges less common. Campbell knew the effectiveness of the rifle and so chose to form up in a line.
How accurate is this? Were the British armed with rifles or muskets, and did this affect Campbell's decision at all?
The 93rd were in the Highland brigade as part of the first division (with the guards brigade). All British army regiments other than those in the 4th division (who still had the 1842 pattern smoothbore) were equipped with the pattern 1851 Minié Rifle.
The pattern 1853 Enfield didn't start to see distribution until the early part of 1855.
There are two schools of thought on Campbells decision to form line rather than square.
I'm not aware of anything he wrote at the time (or later) that sheds any light on it one way or the other.
The 93rd fired at long range (some 600 yards) and then at 250 yards and then by file. When the Russians cavalry split under fire the Grenadier company (on the right of the line) was refused and their volley ended the Russian charge. Although the Russian commander of the Ingermanland Hussars was also convinced that there had to be a larger force hidden over the ridge as otherwise there was no way they would stand in line and so pulled back.
Campbell's rather laconical dispatch on the action can be read at the National Archives