“Underwriting profit,” as respects any one calendar year, means the amount arrived at by deducting from the net earned premiums of that calendar year on ocean marine insurance contracts written within the United States:
(a) Losses incurred.
(b) Expenses incurred.
In arriving at “underwriting profit” there shall not be deducted as expenses incurred an amount exceeding 40 per cent of the gross premiums on ocean marine insurance contracts written during the current calendar year.