Narrative:

It was IFR west flow. I was working a local control position. I had cleared aircraft X for takeoff on runway heading to remain on the frequency for turns (protecting missed approach for parallel runways). I had also cleared aircraft Y for takeoff with a left turn to heading 250. I had issued instructions to aircraft Z to line up and wait. As the aircraft Y aircraft was rolling down the runway; the other local control said they were going around within an aircraft on 2 mile final on the center runway. I offered a 250 heading as an interim to them until they could get in trail of their departure. In doing so; I had to adjust my traffic. Aircraft X was at 2300 ft and more than 3 miles ahead of the left runway arrival so I issued a right turn to heading 290. Immediately after issuing the turn I continued to coordinate with the other local controller as they had said their localizer had gone out and that's why their aircraft went missed approach. I asked if he planned to have multiple misses or not.at this exact same time aircraft Z responded; in a rapid pace; '290 cleared for takeoff' (on replay we didn't notice the cleared for takeoff until the second time listening to it). Then aircraft X asked to confirm heading of 290. I confirmed with aircraft X the 290 heading. At this point aircraft Y aircraft had just rotated. I amended the aircraft Y heading to 270 so that he wasn't a factor with the missed approach going to the 250 heading. I turned aircraft X to a 360 heading; got a readback; and switched them to departure control. I was still not getting a clear answer from the other local control about what their missed approach was doing. I told aircraft Y to remain on the 270 heading and contact departure. The other local controller then tells me they're done with the 250 heading. I then noticed that aircraft Z is rotating off the runway. Looking down at my board; I see that aircraft Z's strip is not angled indicating takeoff clearance issued; and that the next departure strip was not marked to line up and wait. Being caught off guard as to what was going on and not knowing what heading they were going to I said 'aircraft Y turn left heading 250 immediately'. I realized I used the wrong callsign and said 'aircraft Z turn left heading 250 immediately'. Aircraft Z readback the 250 heading. I then turned to the supervisor and said 'I don't think I cleared aircraft Z for takeoff but I may have; either way I'm not sure I will have proper separation and as of right now I don't have route relationship'. I then limited aircraft Z to 3000 ft. Once the aircraft Y climbed out of 4000 ft I turned aircraft Z to a 360 heading. Supervisor tells me to issue a brasher warning to aircraft Z. I climb them to 5000 ft and confirm the 360 heading. I then issue the brasher warning. I'm not sure if there was a loss of separation or not but aircraft Z was never issued a takeoff clearance and I missed a readback.I would have to imagine that had I not been coordinating with the other local controller about a missed approach at the same time; that I would have heard aircraft Z take aircraft X's turn; however as I said in the description we weren't sure what they said the first time we listened to/watched the replay so maybe I wouldn't have. I'm confident that without the coordination going on I would have noticed aircraft Z beginning to roll down the runway.

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Original NASA ASRS Text

Title: ORD Tower Controller reported a loss of separation after an aircraft departed without a takeoff clearance.

Narrative: It was IFR West Flow. I was working a Local control position. I had cleared Aircraft X for takeoff on runway heading to remain on the frequency for turns (protecting missed approach for parallel runways). I had also cleared Aircraft Y for takeoff with a left turn to heading 250. I had issued instructions to Aircraft Z to line up and wait. As the Aircraft Y aircraft was rolling down the runway; the other Local Control said they were going around within an aircraft on 2 mile final on the center runway. I offered a 250 heading as an interim to them until they could get in trail of their departure. In doing so; I had to adjust my traffic. Aircraft X was at 2300 ft and more than 3 miles ahead of the left runway arrival so I issued a right turn to heading 290. Immediately after issuing the turn I continued to coordinate with the other Local controller as they had said their localizer had gone out and that's why their aircraft went missed approach. I asked if he planned to have multiple misses or not.At this exact same time Aircraft Z responded; in a rapid pace; '290 cleared for takeoff' (on replay we didn't notice the cleared for takeoff until the second time listening to it). Then Aircraft X asked to confirm heading of 290. I confirmed with Aircraft X the 290 heading. At this point Aircraft Y aircraft had just rotated. I amended the Aircraft Y heading to 270 so that he wasn't a factor with the missed approach going to the 250 heading. I turned Aircraft X to a 360 heading; got a readback; and switched them to Departure Control. I was still not getting a clear answer from the other Local Control about what their missed approach was doing. I told Aircraft Y to remain on the 270 heading and contact Departure. The other Local Controller then tells me they're done with the 250 heading. I then noticed that Aircraft Z is rotating off the runway. Looking down at my board; I see that Aircraft Z's strip is not angled indicating takeoff clearance issued; and that the next departure strip was not marked to line up and wait. Being caught off guard as to what was going on and not knowing what heading they were going to I said 'Aircraft Y turn left heading 250 immediately'. I realized I used the wrong callsign and said 'Aircraft Z turn left heading 250 immediately'. Aircraft Z readback the 250 heading. I then turned to the supervisor and said 'I don't think I cleared Aircraft Z for takeoff but I may have; either way I'm not sure I will have proper separation and as of right now I don't have route relationship'. I then limited Aircraft Z to 3000 ft. Once the Aircraft Y climbed out of 4000 ft I turned Aircraft Z to a 360 heading. Supervisor tells me to issue a Brasher Warning to Aircraft Z. I climb them to 5000 ft and confirm the 360 heading. I then issue the Brasher Warning. I'm not sure if there was a loss of separation or not but Aircraft Z was never issued a takeoff clearance and I missed a readback.I would have to imagine that had I not been coordinating with the other Local Controller about a missed approach at the same time; that I would have heard Aircraft Z take Aircraft X's turn; however as I said in the description we weren't sure what they said the first time we listened to/watched the replay so maybe I wouldn't have. I'm confident that without the coordination going on I would have noticed Aircraft Z beginning to roll down the runway.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.