B737-700
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 422
Communication Breakdown; Fatigue
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem
Human Factors
Holding number 1; Tower asked us; '[Call sign]; are you taking off VFR today?' We replied 'No.' We did not understand the reason for that unusual question; nor did we query the Tower Controller; nor did the Controller elaborate. We were given a vector for takeoff and instructions to stay with Tower frequency. After takeoff; Tower (or Departure Control after switching; do not remember which); asked us to verify our squawk. We realize at that point we did not enter a squawk and what Tower was covertly implying. We had not done a detailed departure briefing clearance. Fatigue was an issue.While the major fault was not setting a squawk and doing a detailed briefing; Tower appeared they were aware of the error. They could have been handled it in a different or more elaborate manner. Also; Ground Control did not notice us taxiing without a squawk. The ramification was that there was an extra workload in retrieving the squawk and entering it during a higher workload and task saturated environment. Fatigue report submitted.Not cutting corners in presenting briefings assuming procedures were done correctly. Understanding how insidious fatigue onset can be. Query Controlling Agencies as to unusual questions.
I the FO (First Officer) and was out of the flight deck. The Captain received the CPDLC and made inputs on the MCP but forgot to input the squawk; so we were squawking XXXX. No communication from Ground about the squawk. Tower asked us if we were flying VFR. That question didn't make sense to us. On initial climb out; Tower asked us what our squawk was. We then understood and put in the proper squawk. I should have verified all inputs from the clearance. The Ground Controller should have asked us to check our squawk. The Tower Controller should have used proper phraseology.
B737 flight crew reported departing with an incorrect squawk code due to fatigue.