The party is using the traditional comparison of defence dollars measured against the overall size of the economy, which is how all nations benchmark military spending.
The figures suggest that by the time the Conservative government's budget plan is fully implemented in 2027, the country will be spending 0.89 per cent of its gross domestic product on defence.
Currently, it spends roughly 1.02 per cent of GDP on the military, and is under pressure from allies — notably the Americans and British — to meet the NATO standard of two per cent.
Defence Minister Jason Kenney is defending the spending plan, saying the Conservatives have rebuilt the capabilities of the military and increased the National Defence budget by 27 per cent compared to 2006 — a calculation that ignores inflation.
Liberal defence critic Joyce Murray says Kenney further undermines his own credibility by not mentioning that the defence budget was cut by $2.1 billion annually in order to balance the federal books.
"This government hasn't been able to tell the truth on defence," Murray said.
"Their promises of increased funding are not credible in light of (past) promises and cuts. And, even if they were to implement this delayed increase, this would still reduce our military's share of GDP to just point eight per cent, which is unprecedented."
A spokesman for Kenney dismissed the Liberal claims.
"We won't take any lessons on defence spending from the Liberals, who oversaw the 'decade of darkness' where spending was slashed and the procurement of new equipment was non-existent," Daniel Proussalidis said in an email.
"Despite the Liberal spin, Canada continues to punch above its weight in military operations around the world, including those in Iraq and Syria."
He also pointed to a recent parliamentary budget office report that noted the most significant budget cuts took place from 1995 to 2004 under the Liberals.
Dave Perry, an expert with the Canadian Foreign Affairs and Defence Institute, has crunched the same numbers and come up with the same general conclusion, but said the Liberals may actually be too generous in their calculations.
"The numbers the Liberals are estimating on a cash basis for the department are high," said Perry, who pointed to the government's recently tabled departmental plans and performance reports, which have lower projections in the near-term than their Liberal rivals.
In 2008, the Conservatives promised the military "stable and predictable" funding through an annual two per cent increase to their baseline budget — known as an escalator. The government promised in Tuesday's budget to add an extra percentage point to that escalator, starting in 2017.
Whatever the military has gained by the regular increase, it has lost elsewhere through $2.1 billion in deficit-related cuts.
Had the government stuck to what it outlined seven years ago and not included defence in the deficit fight, Perry said the military's appropriation in this budget year would be $3.9 billion higher than what Finance Minister Joe Oliver tabled.
Murray said a Liberal government would do things differently, but did not commit to increasing funding.
Rather, she said, they would craft a clear defence policy that would outline the spending priorities and seek input from not only the opposition, but outside experts.
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