The best narrative of Cumberlege’s life can be found in Target Corinth Canal by Platon Alexiades published in 2015.

The following is taken from Wikipedia at https://en.wikipedia.org/wiki/Mike_Cumberlege –

Lieutenant Commander Claude Michael Bulstrode Cumberlege DSO* RD (26 October 1905 – 1945) was a British Royal Navy officer and Special Operations Executive agent of the Second World War. He was tortured, and eventually executed, by the Germans after being captured while on Operation Locksmith in Greece.

Cumberlege was tasked with undertaking covert and disruptive action in Greece during and after the Battle of Greece. For this purpose, he and his team operated a lightly armed caïque called HMS Dolphin II. In April 1941 Cumberlege secretly navigated the Corinth Canal and laid a time-delayed mine and depth charges; however, the charges failed to detonate. The failure of the mission was a major blow to British intelligence, but in his report the Director of Naval Intelligence went out of his way to exonerate Cumberlege from blame. Shortly after, Cumberlege was ordered to participate in operation Demon, the Allied evacuation from Greece. Dolphin II ferried troops from the beaches of Navplion and Monemvasia to British transports before sailing for Crete. In Canae, Cumberlege met with Captain Nicholas Hammond and Rhodesian private James ‘Jumbo’ Steele, the latter would eventually join him for operation Locksmith. Mike befriended the archaeologist John Pendlebury and they planned to raid the Dodecanese islands but the German airborne invasion of Crete prevented the operation from being carried out. The engines of Dolphin II having given out, Cumberlege commandeered the caique Athanassios Miaoulis and escaped from Crete with his cousin Major Cleland Cumberlege, Hammond, Steele, Able Seaman Saunders and a Greek crew. After they crossed the Kasos Strait they were machine-gunned by a German aircraft, Cleland and Saunders were killed and Mike wounded but they managed to reach Mersa Matruh.

After the Battle of Crete, Cumberlege aided in the evacuation of dozens of Allied personnel who were stranded on occupied Crete. The caïques HMS Escampador and HMS Hedgehog (which were under the command of Cumberlege), successfully rescued 550 Allied troops from the Cretan coast. Once pre-arranged evacuations became impossible, he spent three weeks surreptitiously mapping the deserted south coast of Crete between Cape Litinon and Tsoutsouros Bay, looking for landing beaches and hide-outs for small craft and landing several SOE agents and supplies, without being detected. For this work he was awarded the Distinguished Service Order on 20 January 1942.^] The success of the operations led to the immediate expansion of para-naval SOE operations in the area. In the spring of 1942, Cumberlege took medical leave and spent time in London with his wife and son, before returning to the Mediterranean.

Operation Locksmith

On 8 January 1943, Cumberlege and his SOE team of three others embarked on Operation Locksmith. The operation was a fresh attempt to block the Corinth Canal, applying the lessons which had been learnt from the failed 1941 attempt. Cumberlege was centrally involved in the planning process, and led the mission. On 5 March, having travelled to the canal and set up a hideout, the explosives were placed in the canal. The explosives failed to detonate, and ten days later SOE HQ in Cairo concluded that the mission had failed.

On 19 March, Cumberlege, still at his hideout, reported that he was aware that Italian secret police were searching for his party. In early April, the Abwehr had intercepted signals from a clandestine radio operating in the Hydra area and three patrol boats were sent to triangulate the position. A German patrol was put ashore in the Tselevinia area and Cumberlege’s hideout was discovered. Cumberlege and his group managed to escape, but most of their communications equipment was captured. Three days later the group received a message ostensibly from SOE Cairo that a British submarine was coming to rescue it. On the night of 30 April, the group was captured by German forces who had lured them into a trap using the captured communications equipment.

At the beginning of May 1943, Cumberlege and his colleagues were taken to Averoff Prison in Athens. Despite the German policy of summarily executing captured Allied commandos, Cumberlege was not immediately shot. He was tortured, before being transferred to the Mauthausen-Gusen concentration camp. There, under duress, Cumberlege signed a statement confirming that the Locksmith group were saboteurs – despite having being captured in uniform. In January 1944, Cumberlege was moved to Sachsenhausen concentration camp. He was held in solitary confinement and refused Red Cross parcels. At some point in February 1945 (according to Kurt Eccarius, another witness suggests the date was April 1945), he was executed by the Germans, although the exact date and location are unknown.

Cumberlege was awarded a posthumous Bar to his DSO in 1946 for second attempt to attack the canal.