How do I deal with Terrans turtling in Starcraft 1
I would use corsairs. Use their disruption web either on his bunkers/siege tanks or on his turrets. If you get enough turrets down you could get fliers in the main part of his base which he will not be expecting.
The Downside of Turtling is that while you're building up such pretty defenses the Enemy is being left alone by you so that they can buildup everything they want and go kill the other players. So that means they're asking for top-tech-tier stuff to be shoved down their throat.
Terran Strategy:
Build 5 Battlecruisers and 3 Science Vessels. Do the reactor upgrades and yamato cannon then go in with full energy. Yamato Cannon the Bunkers (5 of them) in the middle, one shot each, then put a Defensive Matrix on several battlecruisers and send them in to finish off the burning bunkers. Retreat and Repeat.
Same deal with the Turrets around the base. You can put Defense Matrix on the Battlecruisers and send them in, if you can shoe-spoon them around the bunkers. You could use the yamato cannon on them but... the best use for the Battlecruisers here is as a distraction so that... you can send in 4 Transports and zerg rush him in his back door (because the turrets will have already selected the cruisers as their target and they will not go after the transports, unless the guy decides to micro, and even if he does by that time they've already done their job). Make the Battlecruisers retreat if they can, but if they cant then bring all of them into the base.
Once you're in the base with your Siege Tanks (thats what you loaded in those transports hopefully) put them in Siege mode and have them go after his Barracks or Factory to stop that annoying unit production. Even if there are turrets still around to fire on your Battlecruisers dont worry about it because he has now lost, unless you do very poorly at your target choice. Use the Yamato against turrets if you have the juice for it. Use the cruisers to attack any units that attack the tanks.
Zergens Strategy:
Send a ton of hydralisks just outside of bombardment range and make them burrow. Then send in 5 Guardians to attack the hardest to access corner of the bunker arrangement (for his sake), which will blow it up, then kill the 4 marines in it. If he sends rienforcements after your guardians, retreat to the Hydras and unburrow them so that your guardians dont turn into meat. Give the guardians time to heal. Burrow the Hydras again (because Siege Tanks are on the way) and then let the Guardians destroy the foolish tanks that are coming. Rinse and Repeat and be sure to continue making these units to rienforce them since they will slowly and steadily die.
Zerg use the Overlords for transport and they only cost Minerals, not Vespine. They may be a viable disposable unit just to get guys into the base (normally you dont think of overlords as being disposable, but in this case they are). The zerg going into the base for this type of zerg rush will die so you wont need those overlords to maintain them. This basically means his turrets are useless unless he truly has tons of them and your overlords cant even drop off the troops. You should have more than one hive for this strategy since you will need fast unit production to replace the Overlords being lost in addition to creating the replacement units. But it should be effective if you send your zergs after the right buildings and avoid the part of the base that has the bombardment zone overlapping it.
Once inside the base focus all of your effort on the Command Center and try to kill any SCVs laying around. All of your guys will die, and you should try to see if you can get a backup squad waiting in the wings to come in and finish the job. You can neutralize any other units at your liesure and this will end the game. If he tries to prolong the agony by ordering his unit production buildings to take off... spawn some Scourge and slam them in transit for some fast murder (or just have the guardians follow them around, and if you can predict where he'll go, move the hydras there in advance).
Protoss Strategy:
Set up the attack with a probe by building a Pilon somewhere near his base but away from the bombardment zone. Build 3 Shield Batteries next to it. Move some Dragoons next to it (5-8 of them) for defense and ambush purposes.
Armed with 5 Carriers and 1 or 2 Arbiters, with all of the relevant upgrades, lay siege to the bunkers. Yes the fighters will be torn apart but they're relatively easy to replace. You use the Arbiters to Stasis the tanks (you might get more than one of them at a time even). If anybody starts getting hit return to the Pilon and battery-up, then go right back in.
It might be a good idea to have 1 or 2 fully stocked Reavers sitting in the wings and if you can manage it another Arbiter. It might just be a good idea to Stasis a bunch of the tanks and bring the Reavers up to blow the crap out of the bunkers. Then use the Carriers on the Tanks instead. Might pull up the Dragoons to their area to handle any response that comes pouring through.
After thats all done send in the Dragoons to focus hit on one or two of the turrets and see if you can get the Carriers into the base through the hole. For any Dragoons who are being attacked by the AI just grab those and send them back to the Battery (then have the Carriers waiting to take out the guys who are chasing them down). Rinse and repeat. It might also be a good idea to send the dragoons in against unit-enabling buildings like the Machine Shop and Armoury, thus surgically removing his ability to create some of the useful stuff. He cant move these anyway and its annoying to have to rebuild them. Also it doesnt take much microing to take out some SCVs with the Dragoons.
In all the chaos this would also be a perfect time for a Reaver Drop, since any turrets in range of your fleet will already be firing on them. Thats alot of damage to just let go unchecked, and if he does start micro against the reavers then he's leaving all that other mess to ruin his day.
Be sure to keep sending Dragoons to the front to help with the fight, and if you lose a couple Carriers replace them up to 4. You should not be losing Arbiters, and if he has air force you use the carriers to destroy the air units. If he does have air force also be wary of that Yamato Cannon sound, and if you hear it move your stuff.
Universal Considerations:
Laying waste to his Siege Tanks and killing the Marines will open up alot of room for him to make more units. When you do get in his base you might think its a good idea to hit the Supply Depots but its not, you wont be able to break enough of the depots to halt his unit production and you will more or less be sitting in his base doing nothing.
If you're playing as Terrans dont go for the nuclear option. The ghosts are too easy to kill and when they're targeting they are exposed, plus the Turrets are going to see them anyway.