This gent and all his antecedents were originally taken from a family tree that mostly looks like my mother's handwriting with some notes about graves from the 1860s in my grandmother's handwriting.  This latter means at least that she checked this tree and thought some notes of validity should be added...
And there is another tree made also by Muriel Ferrand in 1931, from Daphne Briscoe with some subsequent additions by her.
Nevertheless it is to be regarded as material for investigation rather than fact.

One clear lead should be his grandfather who was bishop of Gloucester...

From Burke it looks likely that the Dampier part of his name comes from his maternal first cousin, twice removed's husband, Thomas Dampier, the bishop of Ely.

- TFPL, Dec 1997
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TFPL: Sep 2001:
On an internet site, http://redcoat.future.easyspace.com/offzdiedh.htm, I found a series of entries for army officers and their burials and this included:

'Halifax - Colonel Robert Dampier - 75the Foot - died 1st June 1857.
Son of Rev. Robert and Eliza Hallifax.  Served Kaffir War 1834.  Married Harriet Thomson at Wynberg, Cape Colony, 10th July 1832.
Grave at Karnal - "Here rests the body of Robert Dampier Hallifax, eldest son of the late revd Robert Fitz William Hallifax of Batchcot near Indow Shropshire.  Colonel of H.M. 75th Regt and Brigadier with the Army of Delhie.
Born 28th July 1804.  Died 1st June 1857 aged 52 years." '

I have asked the site owner if he can let me know where he found this gem.

It is possibly in the “Indian Biographical Archive” by Miles Irving and George William de Rhé-Philipe, pub Lahore by the Government Press in 1910.
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TFPL, August 2003:
The army lists for 1850 and 1855-6 show him to have been in the 75th regiment of Foot, "Seringapatam" - The Royal Tiger, superscribed "India".  Seringapatam was a battle fought in Mysore in 1799 against the Tipoo Sultan 'The Tiger of Mysore'.
This regiment was in 1883 attached to the Gordon Highlanders.

An internet correspondent wrote on 26th August 2003:
“The 75th Regt of Foot became known as the Gordfon Highlanders.  Seringapatam was no doubt battle honours respecting the battle of that name in Mysore in 1799 fought against the Tipoo Sultan ‘The Tiger of Mysore’ (Hence the Tiger).  The later duke of Wellington fought there.  ... Karnal is in India about 80 miles from Delhi.”

The Army List for 1850 show his promotion history, with his colonelcy from 1855-6:
1823, 31st July: Ensign
1825, 23 June: Lieut
1826, 8th April: Captain,
1836, 30th July: Major,
1843, 12th December: Lt-Colonel
1854, 20 June: Colonel.

If he did make it to Brigadier, this must have been in the last few months of his life.  Though it sounds as if it was an Indian Army appointment.
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TFPL, Late August 2003:

From the Galway Journal on Thursday October 2nd, 1823 (via http://www.irelandoldnews.com/Galway/1823/OCT.html):

MILITARY PROMOTIONS
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War Office, Sept. 26, 1823.

9th Regiment of Light Dragoons- Thomas John Fitzmaurice, Viscount Kirkwall to be Cornet by purchase, vice Lascelles, promoted to the 67th Foot.
13th Ditto- Lieutenant John Gunn Collins, from half-pay 21st Light Dragoons, to be Lieutenant, vice Meunbury Nash, who exchanges, receiving the difference. George James Christie, Gent, to be Cornet, without purchase, vice Elton promoted.
2d Regiment of Foot-Serjeant Major _____ Littlejohn, from the 72d Foot,to be Ensign, without purchase, vice Munday, promoted, (and to act as Adjt.)
10th Ditto- Lieutenant Charles Collins Blane to be Captain by purchase, vice Rudsdell, promoted. Ensign William Henry Goode to be Lieutenant, by purchase, vice Blane. Robert Dampier Halifax, Gent. to be Ensign, by purchase, vice Goode.  [He was 17 then.]
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The Annual Register for 1843, p. 340 , states that he was in the 75th Foot and promoted from Major to Lt-Col on the 12th December 1843.
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Here’s a thin record from the India Office:

Name: Robert Dampier HALLIFAX
Event type: Biography
Start date:
Start year: 1804
End date:
End year: 1857
Biographical notes: Brev Col, Br Army; de Rhé-Philipe p.146
Transcribed by: British Library
India Office Records Reference:

Source name: de Rhé-Philipe p.146
Source year:
Source edition:
Presidency:
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In the 1841 census he and most of his family were at Sheerness barracks, Isle of Sheppey.  The two eldest daus were with their Thomson grandparents, leaving Robt, by then a Major i/c the garrison depot, Harriet and 4 young children with two staff.
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In the 1911 ensus, there was  John Dampier Hallifax, aged 17 and born in Toronto Canada at the United Services College, Windsor.  Sounds like a grandson, but how?
Also there was a Frederick Plassey Hallifax who was born in Ontario, Canada.
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From the London Gazette:

30 Jul 1836: to be Major, by purchase, in 75th Foot

12 Dec 1843: To be Lieutenant-Colonel, without purchase, in 75th Foot.

22 June 1854: To be Colonel in the Army, in 75th Foot.

11 Sep 1857: Brevet Lt-Col Charles Herbert to be Lt-Col, without purchase, vice Brevet-Col Hallifax, deceased.  Dated 2nd June 1857.
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