Accordingly, the amount of steel tape was increased from two to four layers.[15][17] At Siemens' suggestion, a second supplier, Henleys, was brought in to increase manufacturing capacity.[17] A second test was carried out in June across the Firth of Clyde, with lengths of pipe manufactured by both Siemens and Henleys. The pipe was laid by the Post Office cable ship Iris. Both functioned successfully.[18] Of the 710 nautical miles [nmi] (1,310 km) of Hais cable produced for the operation, 570 nmi (1,060 km) were made by firms in the United Kingdom, while 140 nmi (260 km) was manufactured in the United States by four American firms, including Phelps Dodge and the General Electric Company.[19][20]