Was Due To / Was To: Past Arrangements (C1 Grammar)

Use was / were due to + the base verb for something scheduled for a fixed time on a timetable or calendar.

was / were due to + verb (a scheduled time)

Farid: Is the issue ready to read?
Diego: Not yet. The printer was due to deliver it at nine, but the van broke down.
Not "The vote was due take place on Friday." — say "The vote was due to take place on Friday.". The word to stays after due before the base verb.
Try it: Farid: Why is the ferry still in the harbor? Diego: It ___ at six, but engine trouble kept it in port. Choose the words for the blank. (was due to sail / was due sail / is due to sail) Answer: was due to sail — A fixed time seen from the past takes was due to + base verb, and due keeps its to.

In formal writing, was / were to + base verb gives an official arrangement or outcome; was to have + participle means it fell through.

Farid: Our archive says the old footbridge was to have reopened in May.
Diego: It opened late, but it was to become the best-loved landmark in town.
Not "The minutes record that the vote was to took place on Monday." — say "The minutes record that the vote was to take place on Monday.". After was to, use the base verb: was to take. It is the formal choice for official records.
Try it: Farid: How should I word this line in the history column? Diego: Try this: The treaty ___ reshape the region for a century. Choose the words for the blank. (was to / is to / was due to) Answer: was to — Formal history writing, seen from the past, takes was to + base verb.

Five forms, five flavors: would neutral, was going to a plan, was about to the brink, was due to a schedule, was to formal.

Farid: Did the bus come on time?
Diego: No. It was due to arrive at eight, and we were going to visit the market.
Not "The bus follows a printed schedule, so it was going to come at eight." — say "The bus follows a printed schedule, so it was due to come at eight.". A time fixed by a schedule is was due to; was going to would make it the bus's own plan.
Try it: Farid: Did anyone expect much of the ferryman's son? Diego: Nobody noticed the quiet boy, yet he ___ become the town's most famous painter decades later. Choose the words for the blank. (was to / was due to / was about to) Answer: was to — Looking back at a destiny decades ahead, formal writing uses was to, while "was due to" is a timetable and "was about to" is the brink.

Incorrect	Correct	Why
The vote was due take place on Friday.	The vote was due to take place on Friday.	The word to stays after due before the base verb.
The minutes record that the vote was to took place on Monday.	The minutes record that the vote was to take place on Monday.	After was to, use the base verb: was to take. It is the formal choice for official records.
The bus follows a printed schedule, so it was going to come at eight.	The bus follows a printed schedule, so it was due to come at eight.	A time fixed by a schedule is was due to; was going to would make it the bus's own plan.