So at the very end of the war the Soviets were given some naval vessels and were trained by American instructors.
As Japanese weren't aware of this project, it couldn't be the reason, or even one of the reasons for their capitulation, especially that the end results were no different than results of Soviet earlier attempts:
The operation began at 0500 hours on 17 August. Twenty-one hours later, the strike force entered the First Kuril Strait and took up positions off Capes Kokutan and Kotomari. The first wave, consisting of the naval infantry battalion of some 1.000 men, waded ashore at approximately 0430 hours on 18 August, completely surprising the Japanese.
Even though Japanese resistance was disorganized, the attackers revealed their lack of tactical combat experience and amphibious training as small units made uncoordinated advances inland rather than securing the beach. Within the first hour, Japanese machine-gunners, well emplaced in pillboxes and foxholes, began to inflict heavy casualties.
In addition, belated Soviet attempts to destroy enemy shore batteries our fierce resistance, and Japanese guns soon found the range of the ships off-shore. As Grechko feared, naval gunfire support proved ineffective, in part because of an almost total lack of radio communication with the troops ashore. Asa result, enemy shore batteries wreaked havoc on the amphibious force when it approached at 0530.
'Project Hula : Secret Soviet-American Naval Cooperation in the War Against Japan
Many people believed that Project Hula would have given the Soviet Union the ability to invade the Japanese home islands.
However, many historians agreed it was still not enough for the Soviets to pose a serious threat to Tokyo. As of 20 December 1945, 3,741 American lend-lease ships were given to the Soviets, 36 of which were capable of mounting an invasion of Japan. This was clearly not enough to pose a large threat to Japanese forces in the mainland.
Given how the Soviets conducted in their invasions of southern Sakhalin and the Kuril Islands with limited U.S. Navy ships and landing craft, it was likely that Soviets would not have succeeded in taking entire Japanese-occupied territories, including Hokkaido.
For example, the Soviets in their invasion of southern Sakhalin on August 11 outnumbered the Japanese by a factor of three but they were unable to advance due to strong Japanese resistance. The Soviet invasion of the Kuril Islands took place after Japan's capitulation on August 15, and despite this, the Japanese forces in these islands resisted quite fiercely (although some of them were unwilling to fight due to Japan's surrender on August 15).
In the Battle of Shumshu, the Soviets had 8,821 troops unsupported by tanks and without larger warships. The well-established Japanese garrison had 8,500 troops and fielded around 77 tanks. The Battle of Shumshu lasted for five days in which the Soviets lost over 516 troops and five of the sixteen landing ships (most of these ships were ex-U.S. Navy) to Japanese coastal artillery while the Japanese lost over 256 troops. At the end, Soviet casualties totaled up to 1,567 while the Japanese suffered 1,018 casualties, making it the only battle in the 1945 Soviet-Japanese War where Russian losses exceeded the Japanese.
If the war had actually gone on, the death toll among the Soviets in their invasion of the Kuril Islands would have been far higher and the logistics supply would be severely strained due to lack of Soviet capability to supply its forces and equipment overseas. At the time of Japan's surrender, an estimated 50,000 Japanese soldiers were stationed in Hokkaido. If the Soviets attempted to land at Hokkaido with limited naval capability, it would have run high up to 20,000 Soviet casualties each week, which would have easily destroyed the Soviets' will to wage war against the Japanese.