Construction of the Pinetree Line had only just started when air planners started to have concerns about its capabilities and siting. By the time it detected a potential attack by jet-powered aircraft, there would be little time to do anything before the attack reached Canadian or northern U.S. cities. Additionally the Pinetree systems used "old" pulse-based radars that were fairly easy to jam and were unable to detect targets close to the ground due to scattering. Although expensive in terms of fuel use, it would be possible for Soviet bombers to evade detection by flying lower. They would eventually be seen as they approached the stations, but possibly so late that there would be no possibility of intercepting them. This made the Pinetree Line's usefulness somewhat suspect even before it