Canada is aiming to replace its aging CF-18 Hornets fleet, or what remains of it after nearly three decades of service, and much hangs on what will replace the aircraft.

The planned replacement of the CF-18s, some dating to the early 1980s, coincides with intense discussion on Canada's plans to buy up to 65 F-35 Joint Strike Fighter jets as part of a much delayed air force modernization.

Debate has flared on the F-35's escalating costs and the feasibility of buying the jets when, according to critics, cheaper alternatives are available in the market.

Critics have called for closer scrutiny and suggested alternatives, even the adoption of unmanned aircraft, to fulfill the military's needs. Costs for Canada's F-35 program have fluctuated between $17 billion and $29 billion.

Canada faces no immediate military threat but analysts say both the government and Parliament have been spooked by Russian navy incidents in arctic territories shared with Nordic European countries.

Supporters of a hefty military buildup point out that Canada, as the second largest country in the world after Russia, has much to defend.

However, as the F-35 controversy continues, the debate has widened, questioning the government's stance on the plane's choice. Earlier this month senior officials injected uncertainty into the government's position on the planned purchase.

Plans for replacing the old CF-18 jets tie in with the defense industry's comparative analysis, which places Boeing's Super Hornet ahead of rivals in terms of cost and convenience of integration into a military familiar with Boeing Co. hardware and software.

Canada bought 138 CF-18s in the 1980s but lost some in accidents or retirement. Only about 100 remain but not all of them have been upgraded to be functional. Plans call for all CF-18s to be phased out beginning 2017 and completely by 2020.

The intervening period before the F-35 is bought and phased in will be marked by Canada having a markedly weaker air force. Canadian investment has flowed into the jet's development program but what concerns officials is the escalating cost of the Joint Strike Fighter. No one is able to pinpoint with certainty the final fly-away cost of each of the F-35s that Canada may eventually buy.

Official comments this month hinted Canada may reduce its order if not entirely move from the F-35 to an alternative fighter. Cost worries have led to other NATO member countries indicating they may reduce their orders. The urgency for Canada is to ensure its military remains effectively airborne between the retiring F-18s and the future F-35s.