 Swordfish 's diving depth and time are not known because the records from her sea trials have not survived . Shutting down her boiler , retracting the funnel and sealing the boiler uptake required about a minute and a quarter , which included switching over to the electric motors . In marked contrast to contemporary Vickers designs much attention was paid to safety arrangements , including her extensive subdivision . Indicator and telephone buoys , which could be released from inside the submarine were provided together with external air connections and a charged high @-@ pressure line which could provide air to any manned compartment or the living spaces . Furthermore , the main ballast tanks could be blown from either end of the ship . 
