Yes, there is plenty of historical precedent for this. Taking the British Army as an example, armoured regiments in North Africa were frequently amalgamated as losses were suffered, then split up again as replacements were incorporated. The 3rd & 4th County of London Yeomanry for example, were amalgamated to be known as the 3rd/4th County of London Yeomanry in North Africa and again in Normandy.
In Normandy, another example that springs to mind is the 2nd Battalion of the Essex Regiment, which suffered heavy casualties in three of its four rifle companies during an attack on Lingevres, south of Bayeux. The three mauled companies were then amalgamated into one large company for a few days, until replacements arrived and allowed the battalion to resume its organisation of four rifle companies. Interestingly, the 2nd Essex seems to have performed better in action AFTER incorporating the replacements… That does seem counter-intuitive.
Sidney Jary, in ’18 Platoon’ discusses the platoon-level amalgamations that went on within companies at some length. His platoon spent most of the campaign fighting as two sections, rather than the usual three, with the third Bren kept at platoon HQ, to form a base of fire along with the 2-inch mortar. The company as a whole frequently had only six sections instead of the usual nine.
Taking the other side: German units got smaller and smaller as the Normandy Campaign wore on. They had a deliberate policy of amalgamation until they reached a point where a division was no longer combat-worthy (that point was alarmingly small – many divisions fought on at mere regimental strength). Taking 9th & 10th SS as examples; both divisions suffered heavy casualties in one of the two panzergrenadier regiments in early July 1944 and then amalgamated those regiments into battalion-sized battlegroups. As the bulk of casualties were on the infantrymen, these battlegroups were stuffed with a regiment’s-worth of heavy weapons.
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