As an administrator and organiser the council-pensionary at once applied himself to two most important tasks, financial reform and naval reconstruction.  The burden of debt upon the province of Holland, which had borne so large a part of the charges of the war, was crushing.  The rate of interest had been reduced in 1640 from 6 J to 5 per cent.  But the cost of the English war, which was wholly a naval war, had caused the debt of Holland to mount to 153,000,000 guilders, the interest on which was 7,000,000 guilders per annum.  De Witt first took in hand a thorough overhauling of the public accounts, by means of which he was enabled to check unnecessary outlay and to effect a number of economies.  Finding however that, despite his efforts to reduce expenditure, he could not avoid an annual deficit, the council-pensionary took the bold step of proposing a further reduction of interest from 5 to 4 per cent.  He had some difficulty in persuading the investors in government funds to consent, but he overcame opposition by undertaking to form a sinking fund by which the entire debt should be paid off in 41 years.  Having thus placed the finances of the province on a sound basis, De Witt next brought a similar proposal before the States-General with the result that the interest on the Generality debt was likewise reduced to 4 per cent.

The English war had conclusively proved to the Dutch their inferiority in the size and armament of their war-vessels, and of the need of a complete reorganisation of the fleet.  De Witt lost no time in taking the necessary steps.  The custom which had hitherto prevailed of converting merchantmen into ships of war at the outbreak of hostilities was abandoned.  Steps were taken to build steadily year by year a number of large, strongly-constructed, powerfully armed men-of-war, mounting 60,70 and 80 guns.  These vessels were specially adapted for passing in and out of the shallow waters and were built for strength rather than for speed.  Again, the part taken in the war by the light, swift-sailing English frigates led to a large flotilla of these vessels being built, so useful for scouting purposes and for preying upon the enemy’s commerce.  The supply and training of seamen was also dealt with, and the whole system of pay and of prize-money revised and reorganised.  It was a great and vitally necessary task, and subsequent events were to show how admirably it had been carried out.

No one knew better than John de Witt that peace was the chief interest of the United Provinces, but his lot was cast in troubled times, and he was one of those prescient statesmen who perceive that meekness in diplomacy and willingness to submit to injury do not promote the cause of peace or further the true interests of any country.