It was a year of decisions that heralded the pre-dreadnought era, perhaps the least understood chapter of modern naval history. In March 1889, the Salisbury ministry officially endorsed what later became the Naval Defence Act, which in its final form authorised the largest shipbuilding programme of its kind in the nineteenth century. When it was finally completed five years later, the Royal Navy would have a new fleet based around 10 battleships, 42 cruisers and 18 torpedo gunboats, all of the latest design and at a cost of £21,500,000. Then, in December 1889, the Harrison administration sought legislative approval to adopt a forward offensive naval strategy, complete with a fleet of battleships and armoured cruisers in an unprecedented shift in American naval policy. This strategic rationale provided the intellectual framework to transform the United States into a modern seapower. The purpose of this comparative study is to revisit the decisions of 1889, with the benefit of underutilised archival sources and an innovative research methodology recently embraced by the naval historical community. Whereas prior accounts of these decisions generally assess their historical significance in terms of the naval construction that ensued in the pre-dreadnought era, this thesis focuses instead on the pervasive influence of strategic ideas and how strongly they affected the personalities, institutions and events that shaped the respective outcomes in both London and Washington. That strategic ideas shared among naval officers can be decisive in this regard is the underlying tenet behind the cultural approach to historical naval analysis, which is introduced here to highlight the impact of organisational cultures upon the strategic and force structure choices of military organisations.