We now have ESM contact with the aircraft. Note that even with your own radars off you are still able to maintain the contact, however as time passes an area of ambiguity will develop around the contact, and we will intermittently regain and lose contact.

We're able to maintain contact with the aircraft because we are detecting its radar emissions with our electronic support measures (ESM) equipment. ESM is a passive sensor type that is automatically activated and does not need to be switched on or off. Incoming radar or other emissions are detected and analysed, which depending on the capabilities of the specific ESM set can give a bearing estimate, range estimate, and in this case, specific identification of the emitter--note that after a minute or so of ESM contact we are able to identify the air contact as a Tu-95RT Bear D, a common maritime patrol and reconaissance aircraft with a powerful long range surface search radar.

ESM detections can be made well beyond the maximum range of an emitting radar. Radar sends out radio energy and detects contacts based on their reflection of that energy, but an ESM set only needs to detect the radiated energy--the detected energy doesn't have to be powerful enough to send a reflection for the ESM set to know that there is a contact out there. This is a very important fundamental principle of modern naval and air warfare, and is the main reason why most aircraft and ships prefer to remain EMCON silent (EMCON stands for EMissions CONtrol; EMCON silent means no active emissions) where possible to avoid giving away their presence, identity and location.

Another important concept is that radar energy is directional. Select the air contact and click on 'Contact Report' in the right hand status bar. The omni-directional surface search radar is detected approximately every 10 seconds as it sweeps our destroyer, but the directional Box Tail [PRS-4 Krypton] Tail Warning Radar is only detected when the aircraft is flying away from us. Note that it is detectable even at over 100nm away, despite having an effective range of approximately 10nm--and this is for a relatively weak tail radar!

Now, we know that we are well within detection range for the Bear D's surface search radar, and we have already been emitting our air search radars. It is practically certain that we have been detected, that our identity has been deduced from our radar emissions, and our position has been determined precisely by the Bear D's surface search radar. We also know that for the purposes of our air warfare exercise that we will soon have incoming air threats, so in this tactical situation we will be better served by the situational awareness that our radars give us than the potential to be more stealthy by leaving them off.

Open the Sensors menu (F9) and turn on the SPS-49(V)5 by checking the 'active' box next to its sensor entry. Note that the white air-search range ring around your ship (if the white range ring is not visible, zoom out so you can see at least 260nm from your ship and check that Map Settings > Air Sensors is switched on).