Cyn y rhyfel roedd Thomas Griffiths o Fangor (a anwyd ym 1881) yn gweithio fel saer maen. Fe gytunodd i wasanaethu yn y fyddin ym mis Tachwedd 1915, er na chafodd ei alw i wasanaethu tan 13 Tachwedd 1916. Gwasanaethodd gyda'r 250th Railway Company Royal Engineers, gan dreulio amser yn Ffrainc. Cafodd ei ryddhau o'r fyddin ar 2 Mai 1919. Mae ei ddyddiadur o 1917 mewn ffurf llythyr estynedig i'w wraig, Margaret. Dyma'r tudalennau sy'n adrodd ei hanes ym mis Gorffennaf. Adysgrif: Friday 6/7/17 Heavy firing all night. Bacon 6.00. Work at Mondicourt. Dinner 5.00, bully stew, tea, 1/4 loaf tomorrow jam, poor rations now. Goodnight lovie Saturday 7/7/17 Quiet night. Bacon tea at 6.00. Work at Mondicourt, dinner 5.00 bully stew potatoes, rations 1/4 loafjam. On guard 7.00pm. Quiet night - heavy thunderstorm 2.30am until 6.00am. Sunday 8/7/17 GE No.8 Pay 15 francs (46th) Boiled bacon 7.00am. Pay parade 11.30am. Dinner 12.00 cold bully stew, new potatoes, rice, tea. Thunderstorm again at 12.30pm. Sleep in the afternoon. Rations tomorrow 1/4 loaf. Goodnight dearest one. Monday 9/7/17 Quiet night. Bacon tea at 6.00am. Work at Mondicourt wet and muddy day. Dinner 5.00pm, roast beef potatoes, tea. Tomorrow we are parading at full marching order at 6.25am. Rations 1/2 loaf. Goodnight my lovely. Tuesday 10/7/17 (47th) Parade in full kit at 6.25am. train leaves at 8.45. Arrived Aubigny 11.00am, put up tents and duty over 4.00pm. Tea and nothing with it at 4.30pm. Then went for a stroll to town which is not bad. Had egg & chips, tea in the YMCA & C of E canteen here and you can buy anything here. Goodnight dear one. Wednesday 11/7/17 (48th) Guns firing all night - slept fairly. Grass was damp and no boards. Tonight we have some straw, last night had a fine feed of egg and chips in town. Today was lovely. Goodnight dearest. Thursday 12/7/17 Quiet night. Breakfast 6.15am, bacon & tea. Parade 7.00am. Here dinner 11.30 to 12.15, day over at 4.30pm. Hot dinner 5.00 roast mutton, new potatoes, rice, dates & tea. Lovely weather, rather too hot. One thing would make this life easier to have that is to receive a few lines oftener. Not a line since Friday last. Ta ta love.