Britain's first sea-going iron-clad, was laid down in May 1859, and a further three had been laid down by the end of 1859. Nevertheless, the Royal Navy continued to convert old sailing line-of-battle ships to steam, and to order and lay down new "Bulwark"-class two-deckers. The objective was to achieve parity with the combined navies of France and Russia. Initially there was great uncertainty about the value of iron-clads. So it was prudent to continue building unarmoured steam line-of-battle ships, which would in any case be "the common currency of sea-power for some years to come."