First, it is important to remember that strategic planners didn't have the luxury of planning for a nuclear conflict and a non-nuclear conflict. There was always concern that a war that began conventionally could escalate at anytime into a nuclear war. You always had to consider how to deploy and defend your nuclear assets.

So by the 1980s, Soviet naval doctrine was focused around what came to be known as "bastions," or the "bastion strategy." This is mostly a defensive strategy in which the Soviet Navy will prioritize the defense of its ballistic missile submarines (SSBNs, sometimes called “boomers”), concentrating its naval forces in a relatively small, defensible area within range of friendly land-based aircraft. This will force American/NATO forces (submarines especially) to try and penetrate the web of defenses offered by surface ships armed with ASW (anti-submarine warfare) sensors and anti-ship missiles, smaller aircraft carriers that have helicopters for ASW, conventional and nuclear-powered attack submarines that can attack surface ships and enemy submarines, and land-based fixed-wing aircraft that can carry anti-ship cruise missiles or offer additional ASW capacity. There’s a good map to help you visualize it here, and the article is useful as well. This strategy protects the most important asset in the navy's arsenal -- the boomers -- preserving the Soviets' second-strike ability and nuclear deterrence.

Earlier Soviet SSBNs, such as the Yankee class which came online in the 1960s, lacked the missile range to operate from a "safe" distance of the United States and had to patrol in the Atlantic, passing through the GIUK (Greenland-Iceland-UK) gap where it was likely they'd be detected by NATO ASW operations. The Delta-class boats that followed in the 1970s and 1980s did have the range to remain closer to the Soviet coast, and could thus be protected much more easily. The famous Typhoon-class submarines that entered service late in the Cold War were more advanced. The Soviet strategy began moving this direction in the early 1970s and by the early 1980s was much better prepared to execute this strategy. The most visible proponent was Admiral Sergey Gorshkov, who commanded the Soviet Navy for an extended period during the Cold War.

The Soviet Navy always maintained a large number of submarines, and some earlier strategies were likely more offensively focused. However, the Walker spy ring (perhaps other sources as well, but we know about John Anthony Walker & co.) had delivered information to the Soviets that its submarines were vulnerable and easily tracked by NATO forces. The Soviet Navy in the late 1970s was not insignificant and could project power to establish local superiority for a time, but NATO forces on balance still enjoyed overmatch. It was likely that NATO forces would defeat the Soviet Navy in anything that resembled open battle on the high seas, and basic geography could dictate why naval forces were more important to NATO than the Soviets (only one faction would have to sail large amounts of men and equipment to Europe), but the Soviets continued their naval buildup at this time. Some of this could be explained by a desire to project power to allies in key areas (the Mediterranean or Persian Gulf, perhaps) but its capabilities and focus hinted at another priority: Bastions.

Getting into nuclear strategy would be a bit of a tangent. But speaking broadly, it was understood by both sides that land-based nuclear forces, such as missile silos or bomber bases, could be targeted and destroyed by your enemy’s ICBMs. This meant that submarines were the most survivable leg of the nuclear triad and were the backbone of any “second strike.” If the enemy launched a pre-emptive nuclear attack on you, they might destroy most of your nuclear forces on land, but they couldn’t hit a submarine that was hiding in the ocean. The submarines would still be around to respond, preserving deterrence. Defending these assets was a priority.

The author of this 1981 article argues that the US and NATO should not overlook the possibility that the Soviet navy may be intended for more offensive purposes, but he does a good job of defining the overall concept of the bastion strategy:

The second, more elaborate explanation ties the growth of the Soviet surface fleet to the increasingly important role of the strategic missile submarine (SSBN) within the overall Soviet strategic deterrent. Its proponents submit as evidence (a) the Soviets’ stated naval mission priority of the strategic nuclear strike, (b) Admiral Gorshkov’s insistence that strong surface forces are needed to help protect submarines, (c) the emphasis on antisubmarine armament on the Soviet Fleet’s most recent surface warships, and (d) the regular Soviet practice of combined surface ship and submarine operations. The subordination of the Soviet surface fleet to the security requirements of the SSBN force has been summarized by one author as follows: “The fleet ballistic missile submarine constitute the sword, while the naval air forces (both land and sea-based) and the surface forces constitute the shield, not of the state, but of the sword itself.”

The presence of these bastions is sometimes referenced in modern analyses as a version of anti-access/area denial (A2/AD), an idea that has been resurrected while discussing some aspects of Chinese maritime strategy. In the Atlantic, this area began in the Barents Sea and extended out past the Svalbard Islands into part of the Norwegian Sea, all within range of land-based air support. In the Pacific, the bastion would be the Sea of Okhotsk and perhaps the Sea of Japan, with land-based air support from bases on the Kamchatka Peninsula. To reach these waters and engage the SSBNs, American aircraft, ships, and submarines would have to fight their way through layers of Soviet defenses.

The primary concern would have been American/NATO submarines penetrating the defenses to target Soviet SSBNs. Soviet surface ASW capabilities were designed with the range to engage submarines at the range of American Tomahawk cruise missiles. The Il-38 and Tu-142 land-based aircraft could conduct long-range patrols to defend from NATO submarines. At closer ranges, the Soviet carriers (operating helicopters and VTOL fixed-wing aircraft) could provide another layer of defenses. Meanwhile, attack submarines could also be on station to patrol for any enemies that had maneuvered through defenses. Mines might also be deployed to protect other areas. This isn’t to say that Soviet forces wouldn’t have been able to defend against surface ships or aircraft – Soviet anti-ship missiles at the time were well-respected by their NATO counterparts – but a submarine penetrating the defenses was a real concern.

In many ways, this strategy harkens back to traditional ideas that naval assets serve a strategic purpose, though this is clearly a nuclear-era progression from the idea of sailing a fleet across the oceans to project power. Instead, the Soviet Navy could project power by concentrating its force close to home and withholding its strategic weapons.

There likely would have been some effort to use other submarines, especially those that may have already been forward deployed, to interdict NATO convoys and surface ships, or to hunt SSBNs. The Soviet Navy of the 1980s was capable of walking and chewing gum at the same time. However, the shift that characterized Soviet naval strategy of the era was the emphasis on bastions and layered defenses of the SSBN fleet in waters close enough to the Soviet mainland to receive land-based air support.

In addition to the links above, this 1988 paper by some students at Naval Postgraduate School does a good job of examining the idea of Soviet bastions. This 2014 article in the Naval War College Review examines the 1980s American response to this new Soviet strategy.