Kipling scholars are celebrating the publication of lost poems by the author whose exhortations in "If" to "keep your head when all about you / Are losing theirs and blaming it on you" are regularly voted the nation's favourite poem. Discovered by the American scholar Thomas Pinney in an array of hiding places including family papers, the archive of a former head of the Cunard Line and during renovations at a Manhattan house, more than 50 previously unpublished poems by Rudyard Kipling will be released for the first time next month.

The collection includes several poems dating from the first world war, which Kipling initially supported, helping his son John to gain a commission in the Irish Guards.

A short poem, "The Gambler", finishes with the couplet: "Three times wounded; three times gassed / Three times wrecked – I lost at last", while another fragment runs: "This was a Godlike soul before it was crazed / No matter. The grave makes whole."

After his son's death at the Battle of Loos in 1915, Kipling regretted his earlier enthusiasm for the conflict, writing in his "Epitaphs of the War": "If any question why we died / Tell them, because our fathers lied".

Another poem discovered by Pinney, "The Press", prefigures contemporary worries over media intrusion: "Have you any morals? / Does your genius burn? / Was your wife a what's its name? / How much did she earn?" wrote the poet in a fit of anger at the questions he was asked by journalists. "Why don't you write a play - / Why don't you cut your hair? / Do you trim your toe-nails round / Or do you trim them square?" (The complete poem is reproduced at the foot of this article.)

A discovery in a lighter mood is a stash of comic verse that Kipling wrote on a ship sailing from Adelaide to Ceylon, which is believed to have been read aloud by the author to his fellow passengers. "It was a ship of the P&O / Put forth to sail the sea," wrote Kipling, going on to mourn the slow progress of the liner across the ocean. "The children played on the rotten deck / A monthly growing band / Of sea-bred sin born innocents / That never knew the land."

"Kipling has long been neglected by scholars probably for political reasons," said Pinney, emeritus professor of English at Pomona College in Claremont, California. Despite winning the Nobel prize, Kipling's reputation has suffered over his association with British imperialism – he was described as a "jingo imperialist" by George Orwell, who also called him "the prophet of British Imperialism".

"His texts have never properly been studied but things are starting to change," said Pinney. "There is a treasure trove of uncollected, unpublished and unidentified work out there. I discovered another unrecorded item only recently and that sort of thing will keep happening. It is a tremendously exciting time for scholars and for fans of Kipling."

The 50 unpublished poems are being included alongside more than 1,300 of Kipling's poems in the three-volume Cambridge Edition of The Poems of Rudyard Kipling, the first ever complete edition of his verse, out on 7 March.

"They are all very engaging, and grab you immediately. A lot are very emotional little poems about the war, about his great identification with the ordinary British soldier, and his anger with the authorities," said Linda Bree, arts and literature editorial director at Cambridge University Press.

Bree agreed with Pinney that Kipling, who died in 1936 leaving behind books including The Jungle Book, Just So Stories and Kim, had been neglected by scholars until now. "I think, personally, it's because his poems are very simple. They are about simple situations, and perhaps for that reason scholars have steered clear a little," she said. "Perhaps they speak more clearly to the ordinary reader for that reason. And of course the imperial issue does make things more difficult. [But] he is one of the nation's greatest poets … 'If' is one of the most popular poems in the English language, [and] this edition shows that he wrote much else to entertain, engage and challenge readers."

The Press by Rudyard Kipling

Why don't you write a play –

Why don't you cut your hair?

Do you trim your toe-nails round

Or do you trim them square?

Tell it to the papers,

Tell it every day.

But, en passant, may I ask

Why don't you write a play?

What's your last religion?

Have you got a creed?

Do you dress in Jaeger-wool

Sackcloth, silk or tweed?

Name the books that helped you

On the path you've trod.

Do you use a little g

When you write of God?

Do you hope to enter

Fame's immortal dome?

Do you put the washing out

Or have it done at home?

Have you any morals?

Does your genius burn?

Was you wife a what's its name?

How much did she earn?

Had your friend a secret

Sorrow, shame or vice –

Have you promised not to tell

What's your lowest price?

All the housemaid fancied

All the butler guessed

Tell it to the public press

And we will do the rest.

Why don't you write a play?

[September 1899]

• From The Cambridge Edition of the Poems of Rudyard Kipling, published by Cambridge University Press, £200, reproduced by kind permission of The National Trust for Places of Historic Interest or Natural Beauty

• This article was amended on 27 February 2013. The original said that Thomas Pinney is emeritus professor of English at the University of California. That should have been at Pomona College in Claremont, California, and has been corrected.