 On 31 May , Derfflinger was heavily engaged during the Battle of Jutland , as the second ship in the German battlecruiser line . She sustained 21 major hits during the battle , but dealt considerable damage to the British battlecruiser force as well . At 16 : 26 , HMS Queen Mary sank after a magazine explosion that tore the ship apart ; she had been targeted with a hail of heavy @-@ caliber gunfire from Derfflinger and Seydlitz . Two hours later , at 18 : 30 , HMS Invincible suffered a similar fate , though Derfflinger was assisted by her sister Lützow . During the engagement , Derfflinger had both of her rear turrets knocked out by British gunfire . Her crew suffered 157 men killed and 26 wounded , which was the highest casualty figure for any German ship not sunk . The <unk> of the vessel earned her the nickname " Iron Dog " from her British adversaries . Repair work lasted until 15 October , during which the ship had her pole mast removed and replaced with a tripod mast . The ship conducted training operations until November , at which point she returned to active duty with the fleet . 
