Here is my perspective for what it's worth:
The Navy/Air Force are very capital intensive organizations that make extensive use of hardware/electronics. These pieces of equipment are extremely expensive in terms of costs to the nation (to put things in perspective, 1 submarine of ~ $1 billion = 1000 - 5000 km of new highway construction)
When you put down the money for a new warship, you invest $1 billion with an expectation that it will provide "national security insurance" for 25 years. As threats evolves, the value of this "insurance" diminishes with time and the warship is eventually obsolete in ~ 20 years
So how does one provide continuous "national security insurance" while not bankrupting the nation? The answer is to adopt a mix of:
(1) Brand new warships that can deal with the latest threat perceptions (~ Mirage 2000 to counter PAF F-16s)
(2) 10-15 year old warships that have been upgraded with new sensors/weapons and make up the buld of the fleet (~ BVR equipped Mig-21 Bison Upgrade)
(3) 20-25 year old warships that will probably suffice for patrol duties, anti-piracy, and the most underrated of all naval activities...TRAINING (~ Cannon/R-60 equipped Mig-21 Bis)
The net effect of all this mix of platforms should provide adequete "national security insurance" against Somali Pirates, Pakistani Submarines, Chinese Aircraft Carriers, etc. At the very least, it should provide sufficient deterrance
Now, back to SONAR...
I'd like to have the latest USN / RN ultra-low frequency flank array, towed array SONAR on *ALL* warships. But there are inherent problems:
(1) USN / RuN / RN / FN all maintain fleet ballistic missile submarines that carry their nation's deterrent. Why on earth would they part with their top tier SONAR that can compromise their own deterrent?
(2) Other than the above nations, no one else makes good second tier SONAR with the possible exception of Japan and Germany. All these second tier SONARs are designed by highly paid engineers/scientists and made by highly paid factory workers in first world nations. By default this means first world prices
(3) The life cycle of electronics is significantly shorter than the life cycle of warships. Whereas a warship can be risked in combat for ~ 20 years, the SONAR itself will be of dubious combat value in ~ 10 years
This basically means that SDRE has access only to second tier SONAR capability at exhorbitant prices and need re-capitalization every 10 years at a bare minimum. This will essentially break the bank! Think of how many kms of highway (i.e. drivers of a nation's economy and the well being of its citizens) you can have for that money?
So what is the alternative?
(1) You *must* develop local capability in design and production of electronics. You may start out with a crappy product that can only detect Pakistani Agostas at 3 kms, but the user feedback will give the designer the confidence and knowledge to make iterative improvements and build a product line spanning decades, that will eventually compete with the best
Example: The so called "Poor Quality Asian" Toyota / Honda brands have driven GM / Ford / Chrysler into the ground after 30 years of perseverence. Now Kia is doing the same to Toyota / Honda
How will you ever build a SDRE product line into the league of L3 / Lockheed / Northrop if you give up as soon as the user's reaction to your initial products is "Poor Quality SDRE"???
(2) Remember that the Paulraj's APSOH was better than any second tier SONAR that the british were willig to provide in the 1970s./1980s The HUMSA was the same in the 1990s/2000s. Now that we have more money as a nation, and more "importance" thanks to our nuclear/economic strengths, the west is willing to give us better second tier SONARs that outclass the HUMSA/NAGAN
However, in order to have that western "buy" options continually available to us, we must have comparable desi "make" capabilities. This is the same reason why TSMC charges TI less money to build their chips in TSMC's foundry as compared to say Qualcomm/Broadcom...because TI has an internal "make" capability
Just my 2 cents...