Array that brings a value to a set of mulptiple cells

Hi,

I would like your help with a formula that performs the following calculation in column D. I don't not want to use VBA or a combination of Pivots and Lookups to perform the calculation, I will only need a formula solution. To explain the example of the formula I need,I am using the table below.
Every Record ID has multiple milestones. One of these milestones may have a unique Date plan identified (i.e. OBS1 and OBS 3 have dates but OBS 2 has none). The formula I would like to build will assign the date identified to all milestones corresponding to the same record id. I have previously used an array formula to calculate the same concept but that time instead of dates I was using Boolean values or the same text which was easy to do with an IF(SUM(IF( arrays and statements). In this case the date identified field becomes a new variable and I am not sure how to enter that into my formula.

A- B- C- D
1- ID- Milestone- Date Identified- Formula result
2- OBS1- 1- X- 6/17/2016
3- OBS1- 2- 6/17/2016- 6/17/2016
4- OBS1- 3- X- 6/17/2016
5- OBS2- 1- X-X
6- OBS2- 2- X-X
7- OBS3- 1- X- 7/20/2016
8- OBS3- 2- X- 7/20/2016
9- OBS3- 3- 7/20/2016- 7/20/2016

Sorry couldn't put them in a table. X are blanks and - separate columns
Any help would be greatly appreciated!

Thanks,

Mike

Thank you John, that works!