With the envisaged operational requirements in mind for Operation 'Overlord', involving large forces of Commandos and the possibility of similar commitments elsewhere, it was decided to increase the number of Commandos by raising six more RM Commandos and also to group all these Commandos into Special Service Brigades. As a result the organisation developed from February 1943 into the following format and remained, except for the transfers indicated (*), until the end of the War:

1 Special Service Brigade (later 1 Commando Brigade): consisting of Nos. 3, 4(*), 6, 45 and 46(*) RM Commandos for operations in North-West Europe.

2 Special Service Brigade (later 2 Commando Brigade): consisting of Nos. 2, 9, 40 RM, 41 RM(*) and 43 RM Commandos for operations in Italy, the Adriatic, Albania and Greece.

3 Special Service Brigade (later 3 Commando Brigade): consisting of Nos. 1, 5, 42 RM and 44 RM Commandos for operations in the Far East.

4 Special Service Brigade (later 4 Commando Brigade): consisting of Nos. 41 RM, 46(*), 47, 48 and No. 4(*) Commandos for operations in North-West Europe.

In addition to the above it must be pointed out that detachments from No. 10 (Inter-Allied) Commando operated within all these Brigades, and also prior to D Day provided parties for small scale reconnaissance raids on the coasts of North-West Europe, thus supplementing those carried out by the SBS.

In the spring of 1944 both 1 and 4 SS Brigades began preparing for their respective roles in the invasion of Normandy, launched on 6th June with 1 SS Bde, under the command of 6th Airborne Division, landing on 'Sword' beach with the tasks of capturing the port of Ouistreham and then linking up with the 'Red Devils' to secure the vital bridge over the Orne and the left ferry flank of the Allied invasion.

The Royal Marine Commandos of 4 SS Bde landed to the west of their Army comrades under the command of different Canadian and British divisions on three separate beaches, namely, 'Sword', 'Juno' and 'Gold'.

No. 4 Commando, with two full Troops of French Commandos under command, succeeded in capturing Ouistreham with great dash and élan, whilst the rest of that Brigade fought their way inland to link up with the airborne forces beyond Pegasus Bridge.

Throughout the days - and weeks - that followed the two Commando Brigades fought 'in the line' defending the Amfreville heights and the left flank of the invasion bridgehead, for, after completing their initial tasks to the west from the three beaches mentioned above, 4 SS Bde had regrouped and moved over the Orne to the left flank too. During the ensuing period of protracted defence of this salient position, the subsequent break out and pursuit of the enemy towards the river Seine, lasting no less than 83 days of continuous action, 1 SS Bde was commanded by Lord Lovat until he was seriously wounded on 12th June, when Brigadier Mills-Roberts took over, whilst 4 SS Bde was commanded throughout by Brigadier 'Jumbo' Leicester. Their respective battles and their parts in the liberation of French towns and villages are well marked today with memorials, mostly erected by the local citizens who still annually remember and commemorate their liberation by the Commandos.

Suffice it to add that the casualties suffered by the two Brigades over the period 6th June to 30th September were high, with well over 50% of their overall numbers either killed, seriously wounded or missing.

However, they were sustained by a steady trickle of reinforcements from the Holding Operational Commando (HOC) established in late1943 at Wrexham, where fledgling Commandos, after their initial training at Achnacarry, were posted to undergo further training before drafting to an operational Commando.

However, in spite of these arrangements it was necessary to bring 1 SS Bde back to England for reorganising and re-equipping. Meanwhile 4 SS Bde having been placed under the command of 1 Corps was involved in further operations in the liberation of France, including the crossing of the Seine, at Dunkirk and in the port of Le Havre.