Without the Irish treaty ports (which the United Kingdom had released a year prior to the war), an independent Ireland posed a serious disadvantage to the military capability and safety of British fighting and trade, risking the possibility of invasion if that disadvantage ever proved too great. If Irish sovereignty was to be maintained, then neutrality would have to be steered consciously to the benefit of British interests, as these were its own: at once to aid the British war effort but also to forestall invasion by Britain to regain the treaty ports. Ireland, like other neutrals was '...neutral for the power that potentially threatened them most.' During the war, and accusing de Valera as a 'Nazi sympathiser', the Prime Minister of Northern Ireland, Lord Craigavon, urged Churchill to use Scottish and Welsh troops to overrun 'southern Ireland' before installing a Governor-General for the whole island at Dublin, but this proposal was rejected by London. Nevertheless, Churchill directed Field Marshal Sir Bernard Montgomery to prepare plans to seize Cork and Queenstown (Cobh) so their harbours could be used as naval bases. Better submarine-detecting technology, as well as military bases in Iceland, meant that the Irish ports were no longer as vital for the Allies as they had been during World War I.