St James’s was hit by high explosive and incendiary bombs during the first phase of the London Blitz, at 7.54pm 14 October 1940
 
The blast severely weakened the Church’s brick and Portland Stone fabric: the north wall was fractured and pieces of shrapnel lacerated the building’s east end.

When the smoke cleared, early on 15 October, St James’s was a burnt-out ruin, open to the elements. It remained a roofless shell for nearly seven years. In 1941, services resumed after a temporary roof was constructed over parts of the south aisle. Air raid shelters were used in the Church gardens for the rest of the war.
 
St James’s famous altar carvings, altar piece and organ casing had been protected prior to the raid and survived. Likewise, air raid precautions taken by the staff ensured that the Church's marble font – in which poet and painter William Blake and 18th century Prime Minister William Pitt the Elder had been baptised - also survived.