On January 19, 1915, Germany launched its first-ever air raid against Britain, sending two giant zeppelins across the Channel—“zeps,” in newly coined British slang, progeny of Count Ferdinand von Zeppelin. The raid caused minimal damage but killed four civilians. Another raid followed on January 31, during which nine airships flew as far as Liverpool, along the way sending terrifying shadows scudding across the landscape of Jane Austen’s Pride and Prejudice.
And then came April 22, 1915. Late afternoon, near Ypres; bright sunshine; a light breeze blowing from east to west. The Allied trenches in this sector, or “salient,” were occupied by Canadian and French forces, including a division of Algerian soldiers. The opposing Germans launched an offensive, which as usual began with shelling by distant artillery. This was terrifying enough, and the French and Canadians knew by experience it was a prelude to a head-on infantry attack across no-man’s-land, but at about 5:00 P.M. the look of the battlefield abruptly changed. A gray-green cloud rose from the German side and began drifting across the blasted terrain as German soldiers opened the valves on six thousand tanks filled with over 160 tons of chlorine gas arrayed along a four-mile stretch of the front—the first ever use of lethal gas on a battlefield. As the gas reached the Allied side, its effects were immediate and terrible. Hundreds died at once; thousands ran from their trenches in a panic, many having experienced exposure that would kill them later. Their flight opened an eight-thousand-yard hole in the Allied line, but the effect of the gas attack seemed to surprise even its architects. German soldiers wearing respirators followed the gas cloud, but, instead of surging through the newly opened gap for a decisive victory, dug a new trench line and stayed put. Their commanders, intending mainly to test the gas, had not assembled the necessary reserve forces to take advantage of the opening in the line. Two thousand Canadian soldiers were killed, suffocated as fluid filled their lungs. Wrote one general, “I saw some hundred poor fellows laid out in the open, in the forecourt of a church, to give them all the air they could get, slowly drowning with water in their lungs—a most horrible sight, and the doctors quite powerless.”
But these cataclysms played out on land. Where Room 40 promised to give Britain the clearest advantage was in the battle for control of the seas, and there Britain’s strategy had undergone a change. Its centerpiece remained the destruction of Germany’s fleet in battle, but the Admiralty gave new weight to interrupting the flow of war matériel to Germany and to combating the growing U-boat threat to British commerce. The Admiralty also harbored the persistent fear that Germany might attempt a full-scale invasion of Britain. Clearly any advance warning of German naval actions would be of critical importance.
Room 40 began providing such intelligence almost at once. From November 1914 until the end of the war, according to the group’s William Clarke, “no major movement of the German Fleet could take place without the Admiralty knowing about it some time in advance.” The information was detailed, right down to the movements of individual ships and submarines. But such detail raised a quandary. If the British navy acted in response to every foretold movement of the German fleet, it risked revealing to Germany that its codes had been broken. In a secret internal memorandum, Admiral Oliver wrote that “the risk of compromising the codes ought only to be taken when the result would be worth it.”
But what did “worth it” mean? Some of the men within Room 40 contended that much useful information was stockpiled and never used because the Admiralty staff—meaning Dummy Oliver—had an obsessive fear of revealing the Mystery. For the first two years of the war, even the commander in chief of the British fleet, Sir John Jellicoe, was denied direct access to Room 40’s decrypted intercepts, although he would seem to have been the one officer in the fleet most likely to benefit from the intelligence they conveyed. In fact, Jellicoe would not be formally introduced to the secret of Room 40, let alone given regular access to its intelligence, until November 1916, when the Admiralty, sensing bruised feelings, agreed to let him see a daily summary, which he was to burn after reading.
The tight control over intercepts exercised by Chief of Staff Oliver was also a source of irritation for Room 40’s Commander Hope.