and have become the model for other specialized and noncommercial marine and non-marine mutuals, for example in relation to oil pollution and nuclear risks. Clubs work on the basis of agreeing to accept a shipowner as a member and levying an initial "call" (premium). With the fund accumulated, reinsurance will be purchased; however, if the loss experience is unfavourable one or more "supplementary calls" may be made. Clubs also typically try to build up reserves, but this puts them at odds with their mutual status. Because liability regimes vary throughout the world, insurers are usually careful to limit or exclude American Jones Act liability. Actual total loss and constructive total loss These two terms are used to differentiate the degree of proof that a vessel or cargo has been lost. An actual total loss occurs when the property has been destroyed, or so damaged as to cease to be a thing of the kind insured. A constructive total loss is a situation in which the cost of repairs plus the cost of salvage equal or exceed the value. The use of these terms is contingent on there being property remaining to assess damages, which is not always possible in losses to ships at sea or in total theft situations. In this respect, marine insurance differs from non-marine insurance, with which the insured is required to prove his loss. Traditionally, in law, marine insurance was seen as an insurance of "the adventure", with insurers having a stake and an interest in the vessel and/or the cargo rather than simply an interest in the financial consequences of the subject-matter's survival. CTL - US Navy usage The term "constructive total loss" or CTL was also used by the United States Navy during and after World War II to describe naval vessels that were damaged to such an extent that they were beyond economical repair. This was most often applied to small-type ships (destroyer, patrol boats, landing ships, mine warfare vessels, etc.) in 1945, the last year of the war, many of which were damaged by kamikazes; postwar the term was also used for ships damaged in typhoons. By this time enough ships were available for the war that some could be disposed of if severely damaged. General averages Average in marine insurance terms is "an equitable apportionment among all the interested parties of such an expense or loss". General average stands apart for