The Altalena was an ex USN LST tank landing ship, 100m long, 2000 tons weight
At the time it was carrying 900 Irgun fighters, 5,000 rifles, 250 Bren guns, 5 million bullets, 50 bazookas and 10 Bren gun carriers.
The left wing Israeli PM Ben Gurion ordered the then Lt Yitzhak Rabin to open fire on the right wing Jews on board, who enthusiastically obeyed, killing 16 (almost including future PM Menachem Begin).
With that kind of force, the siege of the Jewish Quarter in Jerusalem could have been lifted, maybe even all of Jerusalem, plus a chunk of the West Bank.
With Jerusalem, the Temple Mount and the Western Wall under full Jewish control already in 1948, Stalin would have offered full support to Israel, vs an angry Vatican and USA, and an enraged Arab world would have attempted to invade in 1957 instead of 1967.