six
o'clock
But from the crests of the rollers I had a look backwards at Blankenberg , and saw the black funnels and upper works of the enemy 's fleet with the lighthouse and the castle behind them , all flushed with the pink glow of the setting sun . Even as I looked there was the boom of a great gun , and then another . I glanced at my watch . It was six o'clock . The time of the ultimatum had expired . We were at war . There was no craft near us , and our surface speed is nearly twice that of our submerged , so I blew out the tanks and our whale-back came over the surface .