As I stated in an earlier post this can only be answered by a military professional. However for whatever it is worth, let met try to analyze what is required in my view. We are only discussing conventional weapons, not WMD, thus strategic forces are excluded from this discussion.
IMHO State of Pakistan has only 4 probable threats to her existence.
East & North East.
India and only India.
Our limited resources will only allow us to maintain a potent deterrent force. Not to invade and capture Indian Territory but to make it too expensive for India to attack Pakistan as they threatened to do in 2002 and again in the aftermath of Bombay attack. Basically we would like to avoid a full scale war which would inevitably result in crossing the nuclear threshold and the resulting devastation.
North & North West.
Afghani Taliban.
It goes without saying that once Taliban re-establish an Islamic Emirate in Afghanistan. Their next objective would be to have a similar state established in Pakistan. They already have a ‘Fifth Column’ in place in Pakistan in the form of TTP and other jehadi groups.
South:
India and USA.
Indian Navy is overwhelming strong and PN needs to seriously re-arm itself to counter this threat to avoid blockage of the vital sea lanes.
If US feels that her interests are seriously compromised in this region ( say a possible threat of nuclear attack on Israel by Pakistan), US would attempt to neutralize Pakistan’s nuclear assets probably thru cruise missiles fired form US warships stationed about 200 miles beyond Pakistan shoreline. Any major attack by US involving land forces can be discounted for the time being.
For this we need a very good anti aircraft/anti missile defense system and long range cruise missile of our own to attack hostile warships.
Internal:
Pakistan is currently in a state of war. Survival of Pakistan State as we know depends upon complete subjugation of all TTP and their jehadi allies. In addition there are anti Pakistan separatist forces such as BLA and Jiyae Sind movement which have to be neutralized.
IMO there is absolutely no justification for the existence of any lashkar, sipahs, jaish or private militia in any form or shape in a sovereign state. Any call for jehad or fatwa can only be thru organs of State else it is a ‘Fitna’ and must be crushed as it represents a
peril to the existence of the State.
Additionally, possibility of religious extremist forces such as Khilafat Movement, Jamaat Dawa, Jaish Mohammed, Lashkar Tayaaba acting as fifth column for Afghan Taliban cannot be ruled out. These outfits are looking to establish a pan Islamic state; their loyalty to the State of Pakistan is therefore doubtful. Activities of anyone overtly or covertly supporting such outfits should be closely monitored and such persons should be considered foreign agents.
Pakistan’s armed forces should therefore be equipped and trained for meeting both the internal & external threats with paramilitary forces trained & armed for meeting internal threats only.
Land forces:
Assuming parity in training & quality of equipment, you need at least 1/3 in number for a credible defense. PA should be strong enough to deny India the possibility of capturing large chunks of Pak territory and use it for bargaining. Therefore 1/3 of the IA would not be enough of a deterrent. Instead Pakistan should aim for 50% in numerical and equipment strength. Also it expected that PA would do a lot of fighting in the mountains of Kashmir and Pak Afghan border, therefore PA needs significant number of mountain and light infantry.
IMO Brigade level forces would be better suited to fighting in the mountainous terrain because valleys are quite narrow; well coordinated attacks/defense by battalion and brigade size forces would probably prove more effective.
Brigades can always be regrouped into Divisions or Corps size concentrations for fighting in the plains of Punjab and deserts of Sind and Rajasthan. I have therefore broken down PA requirement into brigades.
Paramilitary forces should be armed and trained to the level that in addition to dealing with insurgency, act as second line defense should the war break out with India.
Based on the above PA would ideally need:
Manpower.
80 Infantry brigades (15 mountain/light Infantry, 15 mechanized infantry, 45 motorized and 5 air/ heliborn infantry (Commandos/Paras).
20 armored brigades. 30 artillery brigades, 5 anti tank battalions, 10 AD brigades, 20 Army Aviation squadrons.
In all about 650,000 with an equivalent of 30 Divs or about 400,000 actual fighters. India is unlikely to have more than 800,000 thousand fighters or 60 Divs equivalent in the field against Pakistan unless she decides to leaver her North East Frontier totally undefended.
Therefore the above strength should be sufficient to thwart India’s designs.
IMO existing 11 Corps HQ’s should be sufficient for managing the proposed manpower by simply converting some 2 Div corps to 3 Div level.
Hardware.
1,200 to 1500 tanks of T-80/Alkahild class for the Strike Divs and another 1000 tanks of Al Zarrar class for infantry support. 3,000 APC’s and AFIVs. 1000 pieces of 155 mm towed and SP howitzers. 300 MRLS, 500 pieces of Oerlikan/Zsu33 AA guns. 500 TOW armed APCs/Jeeps.1000 pieces of MANPADS to neutralize threat from Indian helo gun ships.
Crotale NG and RBS-70 etc for medium/ low level air defense plus a few batteries of HQ-9 type High altitude AD missiles. Sufficient numbers of RPGs and anti tank guns.
About 250 helos/fixed wing aircraft including at least 2 Squadrons of modern helo gun ships and two squadrons of battlefield observation aircraft, one squadron of light transport planes for liaison and battlefield casualty evacuation.
Paramilitary forces: About 100,000 strong border security forces plus another 100,000 Federal Security personnel to fight insurgency. These to be armed and trained to be at par with PA Light Infantry in fighting ability and armed with some anti tank weapons.
Air Forces:
Main threat from the air would be from India. PAF should therefore be India centric. Some specialized counter insurgency aircraft and Recce capability is also needed. Also need at least 25 C-130 type aircraft so that a Brigade of Commandos can be airlifted in one go.
Indian Air Force is very large and it would be an economic suicide to aim for 50% of IAF strength. However, we must have sufficient quantity of quality fighter aircraft to deny India air superiority over any theatre and also sufficient number of strike aircrafts to interdict major break through of Indian Amour (Cold Start Doctrine).
For this one would need about 1/3 of total IAF strength in over all numbers but close to 50% of IAF strength in front line aircrafts.
Because Pakistan hasn’t got lot width, transport wing, number of helos, refuellers and AWACS can be smaller than 1/3 of IAF corresponding strength. In addition PAF would need a couple of squadrons of subsonic ground attack aircraft such as SU-25 Frogfoot or A-10 to blast out deeply dug in insurgents.
Suggested minimum strength for PAF would be about 22 front line squadrons of fighters /strike aircraft. For example:
4 Squadrons of J-10 B: – Air Superiority role.
6 Squadrons of F-16:– Strike role
10 Squadrons of JF-17:– work horse and CAS.
2 Squadron of A-10:- Counter insurgency and anti tank.
Plus
1 Recce Squadron- RJF-17
1- Squadron of refuellers
1-Squadron of AWACS/ELINT aircrafts.
3 Squadrons of primary trainers (Mashaaq)
3 Squadrons of basic Jet trainers (K-8)
1 Squadron of advanced trainers (L-15)
Shortfall in numerical strength must be complimented with extra hours on training. Therefore PAF needs simulators at each airbase where the pilots can train when not physically flying.
In addition we need at least two squadrons of medium transport (C-130), two squadrons of helos for liaison and support duties. Medium /Low altitude anti aircraft missile defense system such as Crotale NG plus Oerlikon AA Guns for all the air bases and a company of Air Force guards for the defense of each airbase from Indian commandos or Taliban insurgents/ fifth column saboteurs.
In all about 60-70,000 personnel with about 400 front line aircrafts.
Naval Forces:
Naval hardware is extremely expensive and matching IN even on 1/3 in numbers is beyond Pakistan’s resources in the foreseeable future. If we can safeguard a narrow 50-mile strip along our shores, access thru sea can be kept clear.
PN therefore needs to concentrate on acquiring FAC, Corvettes & Mine Hunters and MR assets. Land based aircraft would be used for interdicting major hostile warships. Land based Cruise missiles data linked with AWACS for attacking ships far beyond the shore (US warships attempting to destroy Pak nukes) should also be in place.
Frigates and destroyers can be fewer in number. Blue water defense would be mainly from state of the art Submarines.
Suggested PN strength:
8 missile firing FAC.
8 FAC (Gunboats)
6 Corvettes (600-800 tons)
6 Mine Hunters.
8 Missile firing Frigates
6 Augusta B / U 214 class Submarines equipped with AIP plus 6 Midget Submarines
10 support ships (Oilers, Supply Ships, and Tugs)
10 LMR aircraft (PC-3)
3 Hawkeye class aircraft.
18 Anti Ship Missile firing JF-17
10 Sea Kings for SAR. 14 anti sub helos to go with the Corvettes & Frigates. 10 light helos for liason. 6 King Air type aircraft for inter base transport along the shore.
One brigade of naval marines for interdicting possible assault by the sea from Indian marines. About 35,000 officers and ratings in total.
Being solely an armchair general; cant really say if this would be enough. On paper this looks achievable if we can tighten our belt a little.