If the insurer has transacted ocean marine insurance in this State in each of the three calendar years immediately preceding the year in which a tax return is required to be filed, the tax shall be computed as follows:
(a) Divide the average annual premiums of the insurer from ocean marine insurance written by it in this State during the preceding three calendar years by the average annual premiums of the insurer from all ocean marine insurance written in the United States during such calendar years.
(b) Multiply the insurer’s average annual underwriting profit from ocean marine insurance written within the United States during the preceding three calendar years by the figure derived in (a).
(c) Multiply the amount derived in (b) by 5 percent.
(Added by Stats. 1961, Ch. 740.)