Depreciation rate reduction for specified ships, aircraft and plant limits alternative deduction claims and sets eligibility periods. The amendment lowers the depreciation rate to twenty per cent for ships, aircraft, machinery and plant specified in the substituted sub-section (8B) and defines actual cost as cost reduced by amounts released under section 32AB(6). It creates transitional qualifying periods for assets acquired or installed between 1 April 1987 and 31 March 1988 subject to pre 12 June 1986 contracts or purchase steps and confines entitlement to the previous year relevant to the assessment year commencing 1 April 1989, while allowing government notification to extend qualifying dates. It also prevents claiming section 32AB deductions in the year a section 32A deduction is taken and for the subsequent four years.