Whatever view may be taken of the long-continued arguments among historians and economists over the consistency and self-consciousness of mercantilist policy, it is evident that most English governments in modern times took some interest in the maintenance of the English merchant shipping industry. At the very least, they were anxious to keep the supply of trained seamen at the highest level possible, since the navy could only be manned in wartime by taking great numbers from the merchant service. Until the end of the seventeenth century they also wished to see large reserves of merchant ships to act as auxiliaries to the royal fleet, and especially of large ships which could take part in fighting alongside it. Recognition that the merchant service was the support of the navy provided the continuing thread in maritime policy. In the seventeenth century a growing consciousness of the economic problems associated with the balance of trade, and the enlargement by colonial development of the area over which English commercial legislation could be effective, wove new strands into the motivation of policy. The view became explicit that it was desirable to keep down foreign participation in the carriage of goods in English trade, not only in order to boost English shipping for the benefit of the navy but also to evade the burden on the balance of payments of freight charges due to foreigners. So there were renewed and more carefully thought out efforts to eliminate foreign ships from trades where they could be replaced by English. In the Navigation Acts from 1651 onward, the second approach is clearly embodied along with the first, and during the rest of the seventeenth century there was further legislation against the foreigner and in support of English trade and shipping. But the Navigation Acts were only the precursors of a great wave of discriminatory legislation in all economic fields, which was set in motion when the authority of Parliament was extended after 1688. This found its expression in a whole range of subsidies to individual industries, bounties for exports, prohibitions of imports, protective tariffs and so on, as parliament warmed to the task of aiding English industry and its raw material suppliers, incidentally giving some further privileges to English shipping.