| Reference number | Title | Date |
| MS/525/5/2/11 | Letter from Philip Watts, 10 Chelsea Embankment to [Dugald] Clerk | 3 March 1915 |
| MS/525/6/1/7 | Letter from Phillip Watts, 10 Chelsea Embankment, to Dugald Clerk, 57 & 58 Lincoln's Inn Fields | 3 December 1914 |
| MS/525/5/4/13 | Letter from Sir Philip Watts, 11 Windsor Crescent, Newcastle-on-Tyne, to [Dugald] Clerk | 27 October 1917 |
| MS/525/6/8/21 | Letter from Philip Watts, Elswick Shipyard, Newcastle upon Tyne, to Dugald Clerk, 57-58 Lincoln's Inn Field, London | 11 August 1915 |
| NLB/39/220 | Copy letter from Robert William Frederick Harrison to Sir Philip Watts, Fellow of the Royal Society | 12 December 1908 |
| NLB/39/310 | Copy letter from Robert William Frederick Harrison to Sir Philip Watts, KCB, Fellow of the Royal Society | 16 December 1908 |
| NLB/54/875 | Copy letter from Robert William Frederick Harrison, Assistant Secretary of the Royal Society; to Sir Philip Watts, FRS | 26 October 1917 |
| NLB/62/47 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to Sir Philip Watts, FRS | 23 November 1921 |
| NLB/67/344 | Copy letter from Francis Alexander Towle, Assistant Secretary of the Royal Society; to Sir Philip Watts, KCB, FRS | 8 December 1924 |
| NLB/69/417 | Copy letter from Sir Ernest Rutherford, President of the Royal Society; to Lady Watts | 25 March 1926 |
| MS/525/6/1/1 | 'As to a device for catching submarines': report by Philip Watts | 3 December 1914 |
| MS/525/6/2/26 | Note on the propulsion of submarines by Philip Watts | 1914 [?] |
| MS/525/6/2/27 | Note on the propulsion of submarines by Philip Watts | 1914 [?] |
| EC/1900/16 | Watts, Sir Philip: certificate of election to the Royal Society | |
| RR/25/1 | Referee's report by Philip Watts, on a paper 'Chances of loss of merchant ships' by W S Abell | 10 September 1918 |
| MC/23/443 | Letter from [George J] Stevens, 25 Eastlake [Road], London SE, to [Robert] Harrison, Assistant Secretary, [Royal Society] | 8 July 1908 |