Liberal senator Jim Molan, a former major general in the Australian Army, has warned against relying too heavily on the United States for military support.
Senator Molan has questioned whether the US has the intention or willingness to send forces to its allies' defence, or the capacity to meet its worldwide commitments.
He said US defence spending had dipped to frighteningly low levels and its capability was focused on countering the so-called "four nations and an ideology" - Russia, Iran, China, North Korea and Islamic extremism.
"Do we still hope to see the US cavalry come charging over the hill to save us? The cavalry might be a bit busy," Senator Molan wrote in a piece for the Australian Strategic Policy Institute on Monday.
Senator Molan acknowledged the federal government was spending $200 billion over the next decade to rebuild its military stocks.
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But he cautioned against adopting the "disastrous delusion" that Australia could rely on a "great and powerful friend" in the US, as it had done with the British until a major naval defeat in 1941.
"Australia now needs to match its rearmament program with a brutally realistic national security strategy, not one based on hope and delusion as we did in December 1941," the senator wrote.
"Before anything else, even ships, planes, tanks or personnel, Australia needs realistic strategy. And strategy does not cost."
