'Mercerised' was a British series of naval gunfire bombardments, by light naval vessels, of the German positions on each side of the Corfu Channel, on Corfu island to the west and the port of Sarandë in German-occupied Albania in the east (September 1944).

The undertaking was implemented within the context of the imminent liberation of Corfu by No. 40 (Royal Marine) Commando on 14 October.

In mid-September 1944, Marshal Josip Broz Tito made clear the fact that his relationship with the USSR was closer than that with the Western Allies, and soon after this General Sir Henry Maitland Wilson, the Supreme Allied Commander, Mediterranean Theatre, decided to switch Allied priorities from Yugoslavia to Greece and Albania.

At about this time intelligence reports combined with aerial reconnaissance confirmed that as part of the withdrawal of Generaloberst Alexander Löhr’s Heeresgruppe 'E' from the southern Balkans, the Germans were preparing to evacuate the island of Corfu in the Ionian Sea. The only two escape routes available for any such undertaking were Greek port of Igoumenitsa, which was about to fall into the hands of the Greek resistance forces led by Napoleon Zervas, and the Albanian port of Sarandë, whose importance had already been emphasised by Brigadier G. M. O. Davy, commanding the Land Forces Adriatic on the eastern side of the Adriatic and Ionian Seas. A force based on No. 2 Commando was therefore assembled to harass the Germans in Sarandë and to assist the area’s Albanian partisans.

The intention had initially been for the commandos to operate in this area for between 24 and 48 hours after their landing on 22 September, but at this time the situation appeared so promising that Brigadier R. J. F. Tod, commanding the 2^nd Special Service Brigade, obtained authority to reinforce No. 2 Commando with No. 40 (Royal Marine) Commando and 25-pdr guns of the 111^th Field Regiment, Royal Artillery, in order to attack and capture Sarandë. Then the weather broke and it was not until 9 October that the attack could be launched. The attack led to the capture of the port, in the process taking prisoner some 600 Germans; the number of prisoners taken by the British and Albanians in this area later rose to about 1,000. The two commando units suffered 81 casualties.

As soon as Sarandë had been taken, the British dropped leaflets on Corfu advising the Germans to surrender. On 12 October white flags were seen and two days later No. 40 Commando crossed to Corfu to accept the surrender of what were only a few German stragglers as the bulk of the garrison had been successfully evacuated through Greece while Sarandë was under attack.

British attempts to pursue the German withdrawal to the north through Albania were foiled by the wide-ranging nature of the demolitions carried out by the German rearguards. However, several Long Range Desert Group patrols were dropped in the Albanian mountains and carried out a number of successful demolitions and ambushes, besides directing RAF air attacks onto German targets. The British presence and activities also had the effect of encouraging the Albanian partisans to make direct attacks on the Germans, something which they had previously avoided.