Sir Robert Arbuthnot, 4th Baronet

Following the outbreak of war in 1914, Arbuthnot's slavishly doctrinaire nature proved harmful to his command abilities, particularly during the German raid on Scarborough when he allowed a group of German light cruisers and destroyers to escape without resistance because he had not yet received official orders from Warrender to open fire. Orion's captain, Frederic Charles Dreyer, had his 13.5 inch guns trained on the enemy ships and later claimed that he repeatedly requested permission to fire, but despite the battle having already been joined for several hours, Arbuthnot refused to allow Dreyer to fire before receiving Warrender's explicit order (via flag hoist) to do so. By the time Warrender (attending to other aspects of the battle in HMS King George V) realized the cause of Arbuthnot's reticence and had the order hoisted, the ships had already turned away and escaped.[12]

Arms of the Arbuthnot baronets of Edinburgh

Arbuthnot was appointed commander of the 1st Cruiser Squadron in January 1915, with the obsolete armoured cruiser HMS Defence as his flagship. Admiral John Jellicoe, commanding the Grand Fleet, noted that all was not entirely well with the squadron under Arbuthnot: "Arbuthnot is one of the finest fellows in the world, but somehow can't run a squadron. His ideals are too high and he can't leave people alone." Still, Jellicoe believed, "He would be invaluable when there is fighting. I have the highest opinion of him."[13]

Defence with the admiral on board was sunk at the Battle of Jutland on 31 May 1916, in circumstances described by Admiral of the Fleet Lord Fisher as "a glorious but not a justifiable death".[14] Rear-Admiral Horace Hood commanding the 3rd Battlecruiser Squadron had briefly engaged light cruisers of the German 2nd Scouting Group, damaging several as they steamed away from the High Seas Fleet at high speed during the initial "Run to the North" stage of the battle. Arbuthnot had seen the engagement and impetuously decided to engage the German cruisers at close range before they could escape; he promptly turned his squadron in pursuit, cutting directly across the path of the 1st Battlecruiser Squadron commanded by David Beatty. In the course of this turn, first Defence and then HMS Warrior steamed directly in front of HMS Lion, forcing it to turn sharply, missing collision with it by less than 200 yards. The British battlecruisers were at that time exchanging shells with their German counterparts as they ran north, drawing the Germans towards the main body of the Grand Fleet: Arbuthnot had turned into an area full of falling shells which other ships had been striving to avoid and was blocking Lion's return fire. The third cruiser of his squadron, HMS Duke of Edinburgh, was unable to cross the battlecruiser line, so stayed behind, while the final cruiser, HMS Black Prince, was also too far away to join the mad dash.[15]

Arbuthnot's goal was apparently aggressively to close at high speed with the drifting, crippled German light cruiser Wiesbaden in order to finish her off. In the process, however, his obsolete and poorly armoured ships obstructed any covering fire from Beatty's better-armoured battlecruisers and presented themselves as an easy target for the combined firepower of German Admiral Franz von Hipper's modern battlecruiser squadron. A lieutenant watching aghast from HMS Malaya later noted "When I first saw them, I [knew] they were doomed."[16] Within minutes, Defence was destroyed with all 903 hands in a massive magazine explosion after taking fire from SMS Lützow at close range.[12] Captain Gunther Paschen of Lützow recorded, "From left to right there appears in the field of the periscope a ship, improbably large and close. At the first glance I recognise an old English armoured cruiser and give the necessary orders...Range 76 hm....Five salvoes rapidly follow, of which three straddle: then there was repeated the now familiar sight of a ship blowing up."[17] Captain Georg von Hase of the battlecruiser Derfflinger also spotted Defence, but did not even have time to train his guns before she was blown up by Lützow.

Warrior fought on, but was soon crippled by fifteen shell hits. She was unintentionally saved from impending destruction by the super-dreadnought Warspite, which was forced to turn in circles around Warrior because of a stuck rudder, drawing the enemy fire to herself in the process. While Warspite's heavy armour allowed her to withstand the pounding and return to port under her own power, Warrior used the opportunity to withdraw, limped away with mortal damage, and was allowed to founder while under tow the next day. Black Prince was blown up with the loss of all hands that night after blundering into the main German battle line in the dark, leaving Duke of Edinburgh as the sole vessel in 1st Cruiser Squadron to survive Jutland.

Arbuthnot's unwise 'berserk rush' towards the enemy was likely a result of his impetuous and overzealous nature; Steel & Hart likened Arbuthnot to "a bulldog with its teeth firmly into its prey...as if only he and they existed. No thought of his smoke obfuscating the view of the all-important battlecruisers and dreadnoughts. No thought of what might lie ahead cloaked in the poor visibility. No thought, really, at all, at least as far as can now be judged."[18] Marder speculates that Arbuthnot's rush may have also partially stemmed from his quasi-religious zeal in obeying Grand Fleet standing orders, which did, in fact, call for cruisers to rapidly seek out and report on the position of the enemy main battle fleet, which was not immediately in view.[19] Walter Cowan, captain of the battlecruiser HMS Princess Royal saw the cruisers approaching the German fleet and commented he would "bet anything" it was Arbuthnot.[19] One beneficiary of the fiasco was the destroyer HMS Onslow, which was engaged in a torpedo attack on the German fleet at this time. The more interesting targets Defence, Warrior and then Warspite drew fire away from her, allowing her to escape. Her commander, John Tovey, went on to play a part in the sinking of the German battleship Bismarck in the Second World War.[20]

A memorial plaque was erected to Arbuthnot in St. Giles' Cathedral, Edinburgh.[21] and he was posthumously made a Knight Commander of the Order of the Bath, having been made a Companion already in 1916.