Tonnage tax reserve requirement: mandated allocation of shipping profits and limited uses, with proportionate tax consequences for misuse. A tonnage tax company must credit a prescribed portion of book profit from qualifying ship operations to a Tonnage Tax Reserve Account, may carry forward any shortfall to the next year (subject to limits), and must utilise reserve amounts within eight years for acquisition of new ships or, after amendment, new inland vessels; misutilisation, non utilisation, or early sale of acquired vessels triggers proportionate taxation under the ordinary provisions, and continued failure to create reserves for two consecutive years terminates the tonnage tax option.