Success or failure in battle is determined by several factors, from strategy and military genius, to weaponry and the weather, but ultimately, as the military tactician Carl von Clausewitz acknowledged during the early nineteenth century, ‘superiority of numbers admittedly is the most important factor in the outcome of an engagement’. Clausewitz's treatise On War, however, concerned land-based warfare, although many of its points applied to the sea. It was Julian Corbett who reinvented strategic military studies during the early twentieth century by defining it in relation to maritime theatres. Among his findings, Corbett suggested that although state fleets expanded during the period in question, privateers performed most of the work. Corbett's claim has been little disputed by maritime and naval scholars. The actions of decentralised armed forces were pivotal to the success or failure of military campaigns at sea.

Yet, even the term privateer limits the wide-ranging number of decentralised forces employed by the state between 1500 and 1650. The use of private shipping, manpower and resources was not limited solely to the activities of those described as such. States hired merchant vessels and their crews to increase the size of their fleets, while also often employing them to provision other naval vessels. Both England and France not only provided letters of marque (or congés) to these private vessels in order to aggravate and hinder the enemy but could also integrate them within the state's fleet when it proved necessary. Nor were statesmen dependent on the national resources of their realm to achieve this. As David Trim has shown, ‘Calvinist corsairs’ operated transnationally with Dutch, English and French privateers often carrying letters of marque signed by the leaders of other Protestant nations.

Although construction schemes, coupled with the advancing tactics used in naval warfare as the period progressed, led states to reduce their reliance on private vessels, royal warships were not in great enough abundance to totally replace the hiring of private craft. Besides this, there was no overpowering drive among states to completely oust them from service. In fact, there were justifications to continue employing them. These ships could be quickly mobilised and were generally less costly to repair and replace.