Something that may be of interest.
http://www.defence.gov.au/SE/publications/ForceStructureReview1991_opt.pdf
And what I found enlightening:
Surface Combatant Numbers
2.28 The number of surface combatants and the levels of capability that they should possess depend on the number of tasks that could be expected to be undertaken, the nature of those tasks, and the tactical environment in which they will be conducted.
2.29 The use of pairs of surface combatants to patrol the approaches to Australia between, say, Derby and Tones Strait, could require about eight ships. Simultaneous patrol tasks off the north-east coast and North West Cape could involve a further two. With allowance for refit and maintenance,
a force of 16 surface combatants, with afloat support, would be required to maintain ten on station.
2.30 The protection of Cocos and Christmas Islands, and offshore resource platforms. could require a further four surface combatants, and if required, convoy operations could absorb a further four. A force of twelve surface combatants would be required to maintain these eight on task.
Realistic tasking levels indicate that 16 of the 28 surface combatants should be destroyers or frigates.
Future Destroyers/Frigates
2.31 The last DDG is planned to pay off in 2001, leaving the number of destroyers and frigates then at eleven (one more than the present ten). With the progressive introduction of the ANZACs, the total will rise to 14 in 2005.
Without a continuing ship building program, numbers will start to reduce in 2008, as the first FFG reaches the end of its life.
2.32 Planning to replace the DDGs will proceed on the basis of an ANZAC derivative.
This would also maintain the continuity of Australian shipbuilding, to achieve commonality, to facilitate through life support and training, and to build the number up to 16. ANZAC derivatives could also replace the first four FFGs.
2.33 The AJ\TZAC derivative can utilise the basic ANZAC design concept, but allow for improved capability and future technological developments. The project could start about 1997, allowing first delivery about 2006. This would leave a five year gap between paying off the last DDG and entry into service of the first ANZAC derivative, but this is considered acceptable.
Destroyer Modernisation Refits
2.34 The ADF has for some time followed a program of mid-life modernisations of the destroyer force as a means of providing capability enhancements and life extensions. The modernisation refits, without exception, have been lengthy. Reduced operational availability, together with considerable capital expenditure, have been consequences of these programs.
The concept of mid-life modernisations is not cost effective, and will not continue. More modest capability enhancements, generally achieving similar outcomes, can be undertaken within the ship's normal maintenance cycle.
Future Patrol Vessels
2.35 The Fremantle class patrol boats currently conduct patrol and intercept operations within the Australian fishing zone. They are due to commence paying off in 1997, with all 15 boats being retired by 1999. While their replacement by twelve offshore patrol vessels is proposed, it is unlikely that these could be available before the end of life of the Fremantles.
2.36 It would not be acceptable to suspend the conduct of the important peacetime surveillance and law enforcement activities in the maritime approaches and fishing zone pending the introduction of new offshore patrol vessels. Therefore a life extension, to early next century, for the Fremantles is essential. The project for a future offshore patrol vessel could start about 1997, with first delivery in about 2004.
2.37
The offshore patrol vessels ideally should be less limited by sea state and more heavily armed than the Fremantle class patrol boats. An appropriate command and control system, good communications, surveillance and electronic support measures systems are highly desirable.
Summary
2.38 Specific proposals to develop improved maritime patrol and response capabilities are:
a. Plan for a surface combatant force comprising 16 destroyers/ frigates and twelve offshore patrol vessels early next century.
b. Plan for an ANZAC derivative, with first delivery in about 2006.
c. Give high priority to life of type extension and sensor upgrade of the Fremantle class patrol boats.
d. Plan to bring a replacement offshore patrol vessel into service, with first delivery in about 2004.
e. Discontinue modernisation refits of major surface combatants in favour of capability upgrades within normal refit cycles.
It has often been said that an ANZAC derivative could not have adequately replaced the DDGs but this ignores the modular nature of the MEKO design that concurrently led to the German Type 123 and 124 Frigates and also had a much larger concepts available that would have provided the desired capability even to F-100 levels (i.e. AEGIS and SPY-1F or even SPY-1D)