1916 A.D., September 2nd. A devil in the shape of 14 units covers London's sky.
I found this. It's refering to Boston UK.
In January 1916 Boston had a new menace to contend with as German Zeppelins appeared in the skies over the town. The first raid, which passed over Boston without incident, affected towns in the East Midlands, when 300 bombs were dropped killing 59 people. The next visit from airships, and one which resulted in the most dramatic incident of the war for Bostonians, arrived on the night of September 2nd 1916 when an L23 Zeppelin dropped bombs on Boston for the first time. Of the four bombs which hit the town, the one which struck the Grand Sluice caused the most damage with one member of the lock-keepers family fatally wounded by the blast and several more people injured. Boston could consider itself unlucky in that the Zeppelin involved in the raid had intended to bomb London but was unable to find its target due to bad weather. The raid caused enormous fear in the town and blackout regulations, which previously had been rather vague, were tightened up. In January 1917 four anti-aircraft guns were also stationed in Boston for defence but although Zeppelins continued to pass over the town it was never bombed again.
It wasn't until September 2, 1916 that the British pulled the first airship out of the sky over England in direct air-to-air combat. To beat the sting of fighter aircraft and increased British anti-aircraft ground defenses the Zeppelin company began to develop a special series of rigid airships called Height Climbers that routinely operated at altitudes above 20,000 feet. Cruising at seventy MPH and beyond the top-out range of British fighters, crew members fought oxygen depravation, dizziness, bitter cold, snapped oil lines, congealed oil, frozen radiators, and cracked windows.
And finally this one.
William Leefe-Robinson, flying a BE2c, was the first to shoot down a dirigible over Britain, on the 2nd of September, 1916. The massive fire of the burning airship was visible for over a hundred miles. This was during a raid of twelve naval airships which were, somewhat unusually, accompanied by four army airships. Leefe-Robinson became an instant hero. He survived the war, only to die a month later in the influenza epidemic.
It seems to be refering to airships used in WWI against England. The date seems to mark the first time one was shot down.