Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Episode no. | Title | Director | Writer(s) | Original Air Date (ATV) | Production no. |
| --- | --- | --- | --- | --- | --- |
| 1.0 | " A Case for the Bishop " | Alan Perry | Gerry and Sylvia Anderson | 21 September 1969 | 1.0 |
| 2.0 | " A Question of Miracles " | Leo Eaton | Donald James | 28 September 1969 | 2.0 |
| 3.0 | " To Catch A Spy " | Brian Heard | Pat Dunlop | 5 October 1969 | 4.0 |
| 4.0 | "The Feathered Spies" | Ian Spurrier | Tony Barwick | 12 October 1969 | 3.0 |
| 5.0 | "Last Train to Bufflers Halt" | Alan Perry | Tony Barwick | 19 October 1969 | 5.0 |
| 6.0 | "Hole in One" | Brian Heard | Shane Rimmer | 26 October 1969 | 8.0 |
| 7.0 | "Recall to Service" | Peter Anderson | Pat Dunlop | 2 November 1969 | 7.0 |
| 8.0 | "Errand of Mercy" | Leo Eaton | Tony Barwick | 9 November 1969 | 6.0 |
| 9.0 | "The Deadly Whisper" | Leo Eaton | Donald James | 16 November 1969 | 11.0 |
| 10.0 | "The Cure" | Leo Eaton | Pat Dunlop | 23 November 1969 | 10.0 |
| 11.0 | "School for Spies" | Ken Turner | Donald James | 30 November 1969 | 9.0 |
| 12.0 | "May-Day, May-Day!" | Alan Perry | Bob Kesten | 7 December 1969 | 12.0 |
Question:
What was the original air date (atv) of episode 1?
Answer:
21 September 1969