Expanded from an earlier answer of mine

The order of battle for the Soviet Navy looked quite strong at the start of the war. The Five Year Plans (FYP) and the wider Soviet military expansion had been quite beneficial to Soviet naval construction. The Soviet Navy had begun the thirties with a motley assortment of leftovers from the tsarist battlefleet but the FYPs had called for new construction but also an expansion of harbor facilities. Although the Soviet's heavy units remained antiquated, the FYP included construction of a new class of cruisers (Project 26 and 26bis), modern destroyers, and a large submarine fleet. Additionally, the Molotov-Ribbentrop Pact made the Soviets privy to classified details of German naval construction and allowed them to purchase the incomplete Admiral Hipper-class heavy cruiser Lützow. In addition to the existing construction plans, the Navy entertained visions of a larger blue-water fleet including the Project-23 superbattleships. Yet this vision of a strong and growing Soviet Navy was quite deceptive. Stalin's naval expansion was often incomplete, behind schedule, and unable to surmount major technical hurdles. The result was that the Soviet Union went to war with a very weak navy that could only accomplish limited missions.

Aside from the lack of numerous ports, one of the bigger problems facing the Stalin era's Navy was that it lacked the technical and physical infrastructure to build a massive fleet. Naval construction is often quite technical and it is very difficult to scale up smaller ships into larger ones. By the same token, the interwar Treaty period was one in which there was a a degree of technical innovation in naval construction as the Treaty powers sought to wring the most advantage out of their tonnage limits. Welding, new hull forms, innovations in armor placement, super-heated steam, and a whole host of sundry developments were transforming the world's battlefleets in this period. So not only did Soviet naval architects have to struggle to reach the standards of the tsarist Navy, they also had to play catch-up with the rest of the world.

One expedient solution to this problem was for the Soviets to buy expertise and specialized equipment abroad. Although the USSR was not an ideal buyer from the perspective of other naval powers, the Depression eliminated a number of concerns. Fascist Italy proved to be among the more receptive states to Soviet overtures. The Italians had already sold the USSR plans in the 1920s for what became the first Soviet class of submarines of the post-Civil War period, the Dekabrist-class. This cooperation was extended in 1935 when the USSR contracted to the Italian yard an order for the Project 20 destroyer leader which would pave the way for an indigenous-built class of destroyer leaders. Additionally, the Soviets acquired Italian plans for heavy units like battleships and cruisers as well as Italian machinery for new units under construction in Soviet yards. The Project 26 cruisers, for example, were heavily influenced by the Raimondo Montecuccoli light cruisers in terms of design. While the Italians were the most receptive to Soviet naval overtures, they were not alone. The US firm of Gibbs & Cox presented the Soviets plans for hybrid battleship-carriers to be built in US yards, but this plan as well as designs for more conventional battleships fell through because of State Department objections for Treaty-violating ships to be built in US yards. The French did provide some plans to the Soviets as did German firms before the advent of the Hitler government.

The problem with expedient solutions is that they do not fundamentally resolve underlying issues ans the Soviet naval expansion was not an exception to this. Soviet shipyards had great difficulty in emulating the Project 20 destroyer, Tashkent, and the result was that while the foreign-built ship performed adequately, the ships it was supposed to lead did not. The initial batch of Project 7 destroyers, conventional destroyers built to Italian specifications, suffered teething problems with machinery and sea-keeping and subsequent batches had to be modified (Project 7U) to be suitable for service. Moreover, using foreign designs also inadvertently transmitted the vices of naval constructors' approaches to sets of problems. Italian ship designers gave little thought to seakeeping and favored lighter hulls because they envisioned their primary operational theater to be the Mediterranean. The sleek Italian cruisers and destroyers may have been appealing to Soviet naval chiefs, but these were hull forms that would have to operate in much rougher conditions than the relatively placid Mediterranean. Additionally, while foreigners were willing to part with ships and trade secrets piecemeal, they did not provide the Soviet's a basis for a balanced fleet.

The fits and starts of the FYP's ultimately failed battleship program illustrated this problem. Soviet naval architects were privy to some Italian design principles such as the Pugliese shock-absorbing system but did not have full access to the range of material and equipment needed for a truly modern battleship. Buying designs was easy but implementing them was much harder. The overall design and layout of the Project-23s reflected the Italian Ansaldo firm's approach to battleships design, but also incorporated ideas from Gibbs & Cox. Soviet naval industry could not produce face-hardened armor in the quantities needed nor could it produce turbines of enough power to push the planned Project-23 behemoths to their planned 33 knt. design speed. Eventually the Soviets managed to order turbines from the Swiss firm Brown, Boverie, and Cie which would be placed in the first battleship and then copied by Soviet firms for the later ships. The Soviets also had problems with the main guns of the proposed ships and had initially contracted the Czechoslovakian Skoda works to provide these weapons which would in turn be copied. The German occupation of the country precluded this and it is not entirely clear whether the Soviets had a true backup plan. Two Project-23s were on the slipways during 1938 and two more in 1940, but the Soviets never completed them. Soviet firms were able to deliver at least one of Project-23's 16-inch guns and reported performance indicates a good deal of Italian influence, but there is much evidence to suggest that Soviet industry could not produce these guns in quantity. The Soviets tried and failed to gain German heavy guns during the Molotov-Ribbentrop Pact period as well as equipment needed for heavy ships like range-finders and other sensors. The lead ship of the class, the Sovetsky Soyuz was only partially complete by Barbarossa and never finished during the siege of Leningrad while the Germans managed to capture the incomplete hull of Sovetskaya Ukraina in Nikolayev. The other two ships were cancelled after the invasion and their incomplete hulls repurposed. Examination of Sovetskaya Ukraina showed the ship to be somewhat defective from a design-standpoint and her bow would likely not have been an efficient hull form for high-speeds. Had the Project-23s been completed they would have been an odd Frankenstein of American and Italian hull designs, Italian-inspired protection and guns, German range-finders, and Swiss machinery.

But material and design problems were only some of the dilemmas facing the Soviet Navy as it expanded during the FYPs. There was a degree of human error and muddled strategic thought that filtered into the planning stages that hamstrung construction. The interwar period was a time of real and hypothetical experimentation among naval architects worldwide which provided the Soviet Navy an embarrassment of riches to emulate. Soviet planners toyed with or even tried to implement nearly all of these innovations ranging from French contre-torpilleurs, pocket battleships, treaty-busting super-battleships, aircraft carriers, hybrid battleship-carriers, small and large submarines and a myriad of other possibilities. Not only were these innovations out of the reach of Soviet industry, it muddled Soviet grand naval strategy and long-term planning. The divided Admiralty had very little conception of what type of fleet it wanted to be. Soviet grand naval strategy in the interwar period vacillated between coastal defense tied closely to land, a proactive defensive strategy that required light and medium forces to take the fight to the enemy thus leaving Soviet waters secure, and a blue-water fleet that could make Soviet power visible in the oceans. Stalin's own predilections were for a blue-water fleet, but he also at various times pushed for the other two strategies. Each of these strategic visions necessitated different types of ships, as well as adjustments in doctrine, but there was very little attempt to establish order and priorities. Thus the constructed Soviet fleet of the FYPs tried to do too much with little experience at how to accomplish these constantly shifting goals. Massive expansion spread the Soviet naval officer corps quite thin, and the losses from the Great Purges added yet more difficulties. At a special conference of fleet commanders in December 1940, Soviet naval chief Admiral Kuznetsov put the finger squarely on this problem of the FYPs stating:

There wasn’t a common point of view on principal subjects concerning the Navy’s activity. Exact naval thinking wasn’t taught, while fruitless discussions went on far too long. Those discussions didn’t bring us anything but harm.

Kuznetsov though did not really follow through on his diagnosis and pushed for a blue-water fleet as well as an across the board expansion.