Malcolm Turnbull remarked recently that Australia and the United States remain joined at the hip in matters of defence.

This could be taken as a statement of his government's avowedly pro-Washington political disposition; a template for future strategic policy decisions; or, perhaps as a pragmatic piece of relationship strengthening, given that Australia derives more from the US alliance than America gets in return.

US President Donald Trump announces his strategy on Afghanistan. Credit:AP

Considering a North Korean attack, for example, Australia would enjoy the immediate retaliatory power of the world's largest and most lethal war machine. The deterrent factor of this alone is incalculable.

In truth, Mr Turnbull's observation probably combined all three elements above.